To see the other types of publications on this topic, follow the link: Cortex in visual stimulus.
Journal articles on the topic 'Cortex in visual stimulus'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Cortex in visual stimulus.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Földiák, Peter. "Stimulus optimisation in primary visual cortex." Neurocomputing 38-40 (June 2001): 1217–22. http://dx.doi.org/10.1016/s0925-2312(01)00570-7.
Full text
2
Carandini, M., H. B. Barlow, A. B. Poirson, L. P. O'Keefe, and J. A. Movshon. "Adaptation to Contingencies in Macaque Primary Visual Cortex." Perception 26, no. 1_suppl (August 1997): 106. http://dx.doi.org/10.1068/v970207.
Full textAbstract:
We tested the hypothesis that neurons in the primary visual cortex adapt selectively to contingencies in the attributes of visual stimuli. We recorded from single neurons in macaque V1 and measured the effects of adaptation either to the sum of two gratings (compound stimulus) or to the individual gratings. According to our hypothesis, there would be a component of adaptation that is specific to the compound stimulus. We performed two sets of experiments. In the first set one grating had optimal orientation and the other was orthogonal to it. In the second set the gratings were parallel, differed in spatial frequency, and were both effective in driving the cell. The first set of experiments, but not the second, provided evidence in favour of our hypothesis. In most cells tested with orthogonal gratings, adaptation to the compound stimulus reduced the responses to the compound stimulus more than the responses to the preferred grating. In addition, in most of these experiments the responses to the compound stimulus were reduced more by adaptation to the compound stimulus than by adaptation to the individual gratings. This suggests that a component of adaptation in the experiments with orthogonal gratings was specific to (and caused by) the contingent presence of the two gratings in the compound stimulus.
3
Carandini, Matteo, Horace B. Barlow, Lawrence P. O'keefe, Allen B. Poirson, and J. Anthony Movshon. "Adaptation to contingencies in macaque primary visual cortex." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 352, no. 1358 (August 29, 1997): 1149–54. http://dx.doi.org/10.1098/rstb.1997.0098.
Full textAbstract:
We tested the hypothesis that neurons in the primary visual cortex adapt selectively to contingencies in the attributes of visual stimuli. We recorded from single neurons in macaque V1 and measured the effects of adaptation either to the sum of two gratings (compound stimulus) or to the individual gratings. According to our hypothesis, there would be a component of adaptation that is specific to the compound stimulus. In a first series of experiments, the two gratings differed in orientation. One grating had optimal orientation and the other was orthogonal to it, and therefore did not activate the neuron under study. These experiments provided evidence in favour of our hypothesis. In most cells adaptation to the compound stimulus reduced responses to the compound stimulus more than it reduced responses to the optimal grating, and adaptation to the optimal grating reduced responses to the optimal grating more than it reduced responses to the compound stimulus. This suggests that a component of adaptation was specific to (and caused by) the simultaneous presence of the two orientations in the compound stimulus. To test whether V1 neurons could adapt to other contingencies in the stimulus attributes, we performed a second series of experiments, in which the component gratings were parallel but differed in spatial frequency, and were both effective in activating the neuron under study. These experiments failed to reveal convincing contingent effects of adaptation, suggesting that neurons cannot adapt equally well to all types of contingency.
4
Qin, Wen, and Chunshui Yu. "Neural Pathways Conveying Novisual Information to the Visual Cortex." Neural Plasticity 2013 (2013): 1–14. http://dx.doi.org/10.1155/2013/864920.
Full textAbstract:
The visual cortex has been traditionally considered as a stimulus-driven, unimodal system with a hierarchical organization. However, recent animal and human studies have shown that the visual cortex responds to non-visual stimuli, especially in individuals with visual deprivation congenitally, indicating the supramodal nature of the functional representation in the visual cortex. To understand the neural substrates of the cross-modal processing of the non-visual signals in the visual cortex, we firstly showed the supramodal nature of the visual cortex. We then reviewed how the nonvisual signals reach the visual cortex. Moreover, we discussed if these non-visual pathways are reshaped by early visual deprivation. Finally, the open question about the nature (stimulus-driven or top-down) of non-visual signals is also discussed.
5
Kok, Peter, Michel F. Failing, and Floris P. de Lange. "Prior Expectations Evoke Stimulus Templates in the Primary Visual Cortex." Journal of Cognitive Neuroscience 26, no. 7 (July 2014): 1546–54. http://dx.doi.org/10.1162/jocn_a_00562.
Full textAbstract:
Sensory processing is strongly influenced by prior expectations. Valid expectations have been shown to lead to improvements in perception as well as in the quality of sensory representations in primary visual cortex. However, very little is known about the neural correlates of the expectations themselves. Previous studies have demonstrated increased activity in sensory cortex following the omission of an expected stimulus, yet it is unclear whether this increased activity constitutes a general surprise signal or rather has representational content. One intriguing possibility is that top–down expectation leads to the formation of a template of the expected stimulus in visual cortex, which can then be compared with subsequent bottom–up input. To test this hypothesis, we used fMRI to noninvasively measure neural activity patterns in early visual cortex of human participants during expected but omitted visual stimuli. Our results show that prior expectation of a specific visual stimulus evokes a feature-specific pattern of activity in the primary visual cortex (V1) similar to that evoked by the corresponding actual stimulus. These results are in line with the notion that prior expectation triggers the formation of specific stimulus templates to efficiently process expected sensory inputs.
6
van Es, Daniel, and Tomas Knapen. "Attention Improves Stimulus Encoding in Early Visual Cortex." Journal of Vision 16, no. 12 (September 1, 2016): 1306. http://dx.doi.org/10.1167/16.12.1306.
Full text
7
Hermes, Dora, Kai J. Miller, Brian A. Wandell, and Jonathan Winawer. "Gamma oscillations in visual cortex: the stimulus matters." Trends in Cognitive Sciences 19, no. 2 (February 2015): 57–58. http://dx.doi.org/10.1016/j.tics.2014.12.009.
Full text
8
Mante, Valerio, and Matteo Carandini. "Mapping of Stimulus Energy in Primary Visual Cortex." Journal of Neurophysiology 94, no. 1 (July 2005): 788–98. http://dx.doi.org/10.1152/jn.01094.2004.
Full textAbstract:
A recent optical imaging study of primary visual cortex (V1) by Basole, White, and Fitzpatrick demonstrated that maps of preferred orientation depend on the choice of stimuli used to measure them. These authors measured population responses expressed as a function of the optimal orientation of long drifting bars. They then varied bar length, direction, and speed and found that stimuli of a same orientation can elicit different population responses and stimuli with different orientation can elicit similar population responses. We asked whether these results can be explained from known properties of V1 receptive fields. We implemented an “energy model” where a receptive field integrates stimulus energy over a region of three-dimensional frequency space. The population of receptive fields defines a volume of visibility, which covers all orientations and a plausible range of spatial and temporal frequencies. This energy model correctly predicts the population response to bars of different length, direction, and speed and explains the observations made with optical imaging. The model also readily explains a related phenomenon, the appearance of motion streaks for fast-moving dots. We conclude that the energy model can be applied to activation maps of V1 and predicts phenomena that may otherwise appear to be surprising. These results indicate that maps obtained with optical imaging reflect the layout of neurons selective for stimulus energy, not for isolated stimulus features such as orientation, direction, and speed.
9
K. Aguirre, Geoffrey. "Variation in Temporal Stimulus Integration Across Visual Cortex." Journal of Vision 18, no. 10 (September 1, 2018): 1371. http://dx.doi.org/10.1167/18.10.1371.
Full text
10
Alink, A., C. M. Schwiedrzik, A. Kohler, W. Singer, and L. Muckli. "Stimulus Predictability Reduces Responses in Primary Visual Cortex." Journal of Neuroscience 30, no. 8 (February 24, 2010): 2960–66. http://dx.doi.org/10.1523/jneurosci.3730-10.2010.
Full text
11
Nauhaus, Ian, Laura Busse, Matteo Carandini, and Dario L. Ringach. "Stimulus contrast modulates functional connectivity in visual cortex." Nature Neuroscience 12, no. 1 (November 23, 2008): 70–76. http://dx.doi.org/10.1038/nn.2232.
Full text
12
Larsen, Axel, Kristoffer H. Madsen, Torben E. Lund, and Claus Bundesen. "Images of Illusory Motion in Primary Visual Cortex." Journal of Cognitive Neuroscience 18, no. 7 (July 2006): 1174–80. http://dx.doi.org/10.1162/jocn.2006.18.7.1174.
Full textAbstract:
Illusory motion can be generated by successively flashing a stationary visual stimulus in two spatial locations separated by several degrees of visual angle. In appropriate conditions, the apparent motion is indistinguishable from real motion: The observer experiences a luminous object traversing a continuous path from one stimulus location to the other through intervening positions where no physical stimuli exist. The phenomenon has been extensively investigated for nearly a century but little is known about its neurophysiological foundation. Here we present images of activations in the primary visual cortex in response to real and apparent motion. The images show that during apparent motion, a path connecting the cortical representations of the stimulus locations is filled in by activation. The activation along the path of apparent motion is similar to the activation found when a stimulus is presented in real motion between the two locations.
13
Shim, Won Mok, Yuhong V. Jiang, and Nancy Kanwisher. "Redundancy gains in retinotopic cortex." Journal of Neurophysiology 110, no. 9 (November 1, 2013): 2227–35. http://dx.doi.org/10.1152/jn.00175.2013.
Full textAbstract:
It is widely claimed that interactions among simultaneously presented visual stimuli are suppressive and that these interactions primarily occur when stimuli fall within the same receptive field ( Desimone and Duncan 1995 ). Here, we show evidence for a novel form of interaction between simultaneously presented but distant stimuli that does not fit either pattern. To examine interactions between simultaneously presented stimuli, we measure the response to a single stimulus as a function of whether or not other stimuli are also presented simultaneously, and we further ask how the response to a given stimulus is affected by whether the simultaneously present stimuli are identical or different from each other. Our method reveals a new phenomenon of “redundancy gain:” the visual response to a stimulus is higher when accompanied by identical stimuli than when that stimulus is presented alone, even though the stimuli are displayed in separate visual quadrants. This pattern is observed throughout the visual hierarchy, including V1 and V2, and we show that it is distinct from the well-known simultaneous suppression effect (Kastner et al. 1998). We propose that the redundancy gain in early retinotopic cortex results from feedback from higher visual areas and may underlie perceptual averaging and other ensemble coding phenomena observed behaviorally.
14
Lebedev, Mikhail A., Diana K. Douglass, Sohie Lee Moody, and Steven P. Wise. "Prefrontal Cortex Neurons Reflecting Reports of a Visual Illusion." Journal of Neurophysiology 85, no. 4 (April 1, 2001): 1395–411. http://dx.doi.org/10.1152/jn.2001.85.4.1395.
Full textAbstract:
When a small, focally attended visual stimulus and a larger background frame shift location at the same time, the frame's new location can affect spatial perception. For horizontal displacements on the order of 1–2°, when the frame moves more than the attended stimulus, human subjects may perceive that the attended stimulus has shifted to the right or left when it has not done so. However, that misapprehension does not disable accurate eye movements to the same stimulus. We trained a rhesus monkey to report the direction that an attended stimulus had shifted by making an eye movement to one of the two report targets. Then, using conditions that induce displacement illusions in human subjects, we tested the hypothesis that neuronal activity in the prefrontal cortex (PF) would reflect the displacement directions reported by the monkey, even when they conflicted with the actual displacement, if any, of the attended stimulus. We also predicted that these cells would have directional selectivity for movements used to make those reports, but not for similar eye movements made to fixate the attended stimulus. A population of PF neurons showed the predicted properties, which could not be accounted for on the basis of either eye-movement or frame-shift parameters. This activity, termed report-related, began approximately 150 ms before the onset of the reporting saccade. Another population of PF neurons showed greater directional selectivity for saccadic eye movements made to fixate the attended stimulus than for similar saccades made to report its displacement. In view of the evidence that PF functions to integrate inputs and actions occurring at different times and places, the present findings support the idea that such integration involves movements to acquire response targets, directly, as well as actions guided by less direct response rules, such as perceptual reports.
15
Jiang, Wan, and Barry E. Stein. "Cortex Controls Multisensory Depression in Superior Colliculus." Journal of Neurophysiology 90, no. 4 (October 2003): 2123–35. http://dx.doi.org/10.1152/jn.00369.2003.
Full textAbstract:
Multisensory depression is a fundamental index of multisensory integration in superior colliculus (SC) neurons. It is initiated when one sensory stimulus (auditory) located outside its modality-specific receptive field degrades or eliminates the neuron's responses to another sensory stimulus (visual) presented within its modality-specific receptive field. The present experiments demonstrate that the capacity of SC neurons to engage in multisensory depression is strongly dependent on influences from two cortical areas (the anterior ectosylvian and rostral lateral suprasylvian sulci). When these cortices are deactivated, the ability of SC neurons to synthesize visual-auditory inputs in this way is compromised; multisensory responses are disinhibited, becoming more vigorous and in some cases indistinguishable from responses to the visual stimulus alone. Although obtaining a more robust multisensory SC response when cortex is nonfunctional than when it is functional may seem paradoxical, these data may help explain previous observations that the loss of these cortical influences permits visual orientation behavior in the presence of a normally disruptive auditory stimulus.
16
Miller, Brian T., Jason Vytlacil, David Fegen, Suraj Pradhan, and Mark D'Esposito. "The Prefrontal Cortex Modulates Category Selectivity in Human Extrastriate Cortex." Journal of Cognitive Neuroscience 23, no. 1 (January 2011): 1–10. http://dx.doi.org/10.1162/jocn.2010.21516.
Full textAbstract:
Different categories of visual objects evoke distinct stimulus-evoked sensory responses in extrastriate visual cortex. Although numerous lines of evidence support a distinct representational neural architecture, the mechanisms underlying the modulation of the category selectivity by top–down influences remains uncertain. In this study, we investigate the causal role of the PFC in the modulation of evoked activity to face and scene stimuli in the extrastriate cortex. We used two experimental approaches to disrupt prefrontal cortical function—repetitive TMS to PFC in healthy participants (Experiment 1) and focal PFC lesions in stroke patients (Experiment 2). After these perturbations to normal PFC function (pre- vs. post-TMS and lesion vs. intact hemisphere), stimulus-evoked activity in extrastriate cortex exhibited less distinct category selectivity to faces and scenes. These two experiments provide convergent evidence highlighting a direct role of PFC in the top–down modulation of bottom–up visual signals.
17
Bányai, Mihály, Andreea Lazar, Liane Klein, Johanna Klon-Lipok, Marcell Stippinger, Wolf Singer, and Gergő Orbán. "Stimulus complexity shapes response correlations in primary visual cortex." Proceedings of the National Academy of Sciences 116, no. 7 (January 28, 2019): 2723–32. http://dx.doi.org/10.1073/pnas.1816766116.
Full textAbstract:
Spike count correlations (SCCs) are ubiquitous in sensory cortices, are characterized by rich structure, and arise from structured internal dynamics. However, most theories of visual perception treat contributions of neurons to the representation of stimuli independently and focus on mean responses. Here, we argue that, in a functional model of visual perception, featuring probabilistic inference over a hierarchy of features, inferences about high-level features modulate inferences about low-level features ultimately introducing structured internal dynamics and patterns in SCCs. Specifically, high-level inferences for complex stimuli establish the local context in which neurons in the primary visual cortex (V1) interpret stimuli. Since the local context differentially affects multiple neurons, this conjecture predicts specific modulations in the fine structure of SCCs as stimulus identity and, more importantly, stimulus complexity varies. We designed experiments with natural and synthetic stimuli to measure the fine structure of SCCs in V1 of awake behaving macaques and assessed their dependence on stimulus identity and stimulus statistics. We show that the fine structure of SCCs is specific to the identity of natural stimuli and changes in SCCs are independent of changes in response mean. Critically, we demonstrate that stimulus specificity of SCCs in V1 can be directly manipulated by altering the amount of high-order structure in synthetic stimuli. Finally, we show that simple phenomenological models of V1 activity cannot account for the observed SCC patterns and conclude that the stimulus dependence of SCCs is a natural consequence of structured internal dynamics in a hierarchical probabilistic model of natural images.
18
Alwis, Dasuni S., Katrina L. Richards, and Nicholas S. C. Price. "Masking reduces orientation selectivity in rat visual cortex." Journal of Neurophysiology 116, no. 5 (November 1, 2016): 2331–41. http://dx.doi.org/10.1152/jn.00366.2016.
Full textAbstract:
In visual masking the perception of a target stimulus is impaired by a preceding (forward) or succeeding (backward) mask stimulus. The illusion is of interest because it allows uncoupling of the physical stimulus, its neuronal representation, and its perception. To understand the neuronal correlates of masking, we examined how masks affected the neuronal responses to oriented target stimuli in the primary visual cortex (V1) of anesthetized rats ( n = 37). Target stimuli were circular gratings with 12 orientations; mask stimuli were plaids created as a binarized sum of all possible target orientations. Spatially, masks were presented either overlapping or surrounding the target. Temporally, targets and masks were presented for 33 ms, but the stimulus onset asynchrony (SOA) of their relative appearance was varied. For the first time, we examine how spatially overlapping and center-surround masking affect orientation discriminability (rather than visibility) in V1. Regardless of the spatial or temporal arrangement of stimuli, the greatest reductions in firing rate and orientation selectivity occurred for the shortest SOAs. Interestingly, analyses conducted separately for transient and sustained target response components showed that changes in orientation selectivity do not always coincide with changes in firing rate. Given the near-instantaneous reductions observed in orientation selectivity even when target and mask do not spatially overlap, we suggest that monotonic visual masking is explained by a combination of neural integration and lateral inhibition.
19
Rittenhouse, Cynthia D., Beth A. Siegler, Courtney A. Voelker, Harel Z. Shouval, Michael A. Paradiso, and Mark F. Bear. "Stimulus for Rapid Ocular Dominance Plasticity in Visual Cortex." Journal of Neurophysiology 95, no. 5 (May 2006): 2947–50. http://dx.doi.org/10.1152/jn.01328.2005.
Full textAbstract:
Although it has been known for decades that monocular deprivation shifts ocular dominance in kitten striate cortex, uncertainty persists about the adequate stimulus for deprivation-induced losses of cortical responsiveness. In the current study we compared the effects of 2 days of lid closure and 2 days of monocular blur using an overcorrecting contact lens. Our finding of comparable ocular dominance shifts in visual cortex indicates that deprived-eye response depression is not a result of reduced retinal illumination. The quality rather than the quantity of retinal illumination is the key factor for ocular dominance plasticity. These data have implications for both the mechanism and treatment of amblyopia.
20
Nardo, Davide, Valerio Santangelo, and Emiliano Macaluso. "Audiovisual stimulus-driven contributions to spatial orienting in ecologically valid situations: An fMRI study." Seeing and Perceiving 25 (2012): 16. http://dx.doi.org/10.1163/187847612x646389.
Full textAbstract:
Mechanisms of audiovisual attention have been extensively investigated, yet little is known about their functioning in ecologically-valid situations. Here, we investigated brain activity associated with audiovisual stimulus-driven attention using naturalistic stimuli. We created 120 short videos (2.5 s) showing scenes of everyday life. Each video included a visual event comprising a lateralized (left/right) increase in visual saliency (e.g., an actor moving an object), plus a co-occurring sound either on the same or the opposite side of space. Subjects viewed the videos with/without the associated sounds, and either in covert (central fixation) or overt (eye-movements allowed) viewing conditions. For each stimulus, we used computational models (‘saliency maps’) to characterize auditory and visual stimulus-driven signals, and eye-movements (recorded in free viewing) as a measure of the efficacy of these signals for spatial orienting. Results showed that visual saliency modulated activity in the occipital cortex contralateral to the visual event; while auditory saliency modulated activity in the superior temporal gyrus bilaterally. In the posterior parietal cortex activity increased with increasing auditory saliency, but only when the auditory stimulus was on the same side as the visual event. The efficacy of the stimulus-driven signals modulated activity in the visual cortex. We conclude that: (1) audiovisual attention can be successfully investigated in real-like situations; (2) activity in sensory areas reflects a combination of stimulus-driven signals (saliency) and their efficacy for spatial orienting; (3) posterior parietal cortex processes auditory input as a function of its spatial relationship with the visual input.
21
Hsieh, P. J., J. T. Colas, and N. Kanwisher. "Spatial pattern of BOLD fMRI activation reveals cross-modal information in auditory cortex." Journal of Neurophysiology 107, no. 12 (June 15, 2012): 3428–32. http://dx.doi.org/10.1152/jn.01094.2010.
Full textAbstract:
Recent findings suggest that neural representations in early auditory cortex reflect not only the physical properties of a stimulus, but also high-level, top-down, and even cross-modal information. However, the nature of cross-modal information in auditory cortex remains poorly understood. Here, we used pattern analyses of fMRI data to ask whether early auditory cortex contains information about the visual environment. Our data show that 1) early auditory cortex contained information about a visual stimulus when there was no bottom-up auditory signal, and that 2) no influence of visual stimulation was observed in auditory cortex when visual stimuli did not provide a context relevant to audition. Our findings attest to the capacity of auditory cortex to reflect high-level, top-down, and cross-modal information and indicate that the spatial patterns of activation in auditory cortex reflect contextual/implied auditory information but not visual information per se.
22
Sergent, Claire, Christian C. Ruff, Antoine Barbot, Jon Driver, and Geraint Rees. "Top–Down Modulation of Human Early Visual Cortex after Stimulus Offset Supports Successful Postcued Report." Journal of Cognitive Neuroscience 23, no. 8 (August 2011): 1921–34. http://dx.doi.org/10.1162/jocn.2010.21553.
Full textAbstract:
Modulations of sensory processing in early visual areas are thought to play an important role in conscious perception. To date, most empirical studies focused on effects occurring before or during visual presentation. By contrast, several emerging theories postulate that sensory processing and conscious visual perception may also crucially depend on late top–down influences, potentially arising after a visual display. To provide a direct test of this, we performed an fMRI study using a postcued report procedure. The ability to report a target at a specific spatial location in a visual display can be enhanced behaviorally by symbolic auditory postcues presented shortly after that display. Here we showed that such auditory postcues can enhance target-specific signals in early human visual cortex (V1 and V2). For postcues presented 200 msec after stimulus termination, this target-specific enhancement in visual cortex was specifically associated with correct conscious report. The strength of this modulation predicted individual levels of performance in behavior. By contrast, although later postcues presented 1000 msec after stimulus termination had some impact on activity in early visual cortex, this modulation no longer related to conscious report. These results demonstrate that within a critical time window of a few hundred milliseconds after a visual stimulus has disappeared, successful conscious report of that stimulus still relates to the strength of top–down modulation in early visual cortex. We suggest that, within this critical time window, sensory representation of a visual stimulus is still under construction and so can still be flexibly influenced by top–down modulatory processes.
23
Haile, Theodros M., Kaitlin S. Bohon, Maria C. Romero, and Bevil R. Conway. "Visual stimulus-driven functional organization of macaque prefrontal cortex." NeuroImage 188 (March 2019): 427–44. http://dx.doi.org/10.1016/j.neuroimage.2018.11.060.
Full text
24
Beck, Diane M., and Sabine Kastner. "Stimulus similarity modulates competitive interactions in human visual cortex." Journal of Vision 7, no. 2 (August 27, 2007): 19. http://dx.doi.org/10.1167/7.2.19.
Full text
25
Serences, John T., Edward F. Ester, Edward K. Vogel, and Edward Awh. "Stimulus-Specific Delay Activity in Human Primary Visual Cortex." Psychological Science 20, no. 2 (February 2009): 207–14. http://dx.doi.org/10.1111/j.1467-9280.2009.02276.x.
Full text
26
Hermes, D., K. J. Miller, B. A. Wandell, and J. Winawer. "Stimulus Dependence of Gamma Oscillations in Human Visual Cortex." Cerebral Cortex 25, no. 9 (May 22, 2014): 2951–59. http://dx.doi.org/10.1093/cercor/bhu091.
Full text
27
Roth, Zvi, David Heeger, and Elisha Merriam. "Stimulus vignetting and orientation selectivity in human visual cortex." Journal of Vision 18, no. 10 (September 1, 2018): 1052. http://dx.doi.org/10.1167/18.10.1052.
Full text
28
King, Jillian L., and Nathan A. Crowder. "Adaptation to stimulus orientation in mouse primary visual cortex." European Journal of Neuroscience 47, no. 4 (February 2018): 346–57. http://dx.doi.org/10.1111/ejn.13830.
Full text
29
Martinez, Luis M., José‐Manuel Alonso, R. Clay Reid, and Judith A. Hirsch. "Laminar processing of stimulus orientation in cat visual cortex." Journal of Physiology 540, no. 1 (April 2002): 321–33. http://dx.doi.org/10.1113/jphysiol.2001.012776.
Full text
30
Manahova, Mariya E., Pim Mostert, Peter Kok, Jan-Mathijs Schoffelen, and Floris P. de Lange. "Stimulus Familiarity and Expectation Jointly Modulate Neural Activity in the Visual Ventral Stream." Journal of Cognitive Neuroscience 30, no. 9 (September 2018): 1366–77. http://dx.doi.org/10.1162/jocn_a_01281.
Full textAbstract:
Prior knowledge about the visual world can change how a visual stimulus is processed. Two forms of prior knowledge are often distinguished: stimulus familiarity (i.e., whether a stimulus has been seen before) and stimulus expectation (i.e., whether a stimulus is expected to occur, based on the context). Neurophysiological studies in monkeys have shown suppression of spiking activity both for expected and for familiar items in object-selective inferotemporal cortex. It is an open question, however, if and how these types of knowledge interact in their modulatory effects on the sensory response. To address this issue and to examine whether previous findings generalize to noninvasively measured neural activity in humans, we separately manipulated stimulus familiarity and expectation while noninvasively recording human brain activity using magnetoencephalography. We observed independent suppression of neural activity by familiarity and expectation, specifically in the lateral occipital complex, the putative human homologue of monkey inferotemporal cortex. Familiarity also led to sharpened response dynamics, which was predominantly observed in early visual cortex. Together, these results show that distinct types of sensory knowledge jointly determine the amount of neural resources dedicated to object processing in the visual ventral stream.
31
Tjan, Bosco S., Vaia Lestou, and Zoe Kourtzi. "Uncertainty and Invariance in the Human Visual Cortex." Journal of Neurophysiology 96, no. 3 (September 2006): 1556–68. http://dx.doi.org/10.1152/jn.01367.2005.
Full textAbstract:
The way in which input noise perturbs the behavior of a system depends on the internal processing structure of the system. In visual psychophysics, there is a long tradition of using external noise methods (i.e., adding noise to visual stimuli) as tools for system identification. Here, we demonstrate that external noise affects processing of visual scenes at different cortical areas along the human ventral visual pathway, from retinotopic regions to higher occipitotemporal areas implicated in visual shape processing. We found that when the contrast of the stimulus was held constant, the further away from the retinal input a cortical area was the more its activity, as measured with functional magnetic resonance imaging (fMRI), depended on the signal-to-noise ratio (SNR) of the visual stimulus. A similar pattern of results was observed when trials with correct and incorrect responses were analyzed separately. We interpret these findings by extending signal detection theory to fMRI data analysis. This approach reveals the sequential ordering of decision stages in the cortex by exploiting the relation between fMRI response and stimulus SNR. In particular, our findings provide novel evidence that occipitotemporal areas in the ventral visual pathway form a cascade of decision stages with increasing degree of signal uncertainty and feature invariance.
32
Park, Sunyoung, and Won Mok Shim. "Stimulus predictability affects reconstruction of dynamic visual objects in early visual cortex." Journal of Vision 18, no. 10 (September 1, 2018): 347. http://dx.doi.org/10.1167/18.10.347.
Full text
33
Stenner, Max-Philipp, Markus Bauer, Patrick Haggard, Hans-Jochen Heinze, and Ray Dolan. "Enhanced Alpha-oscillations in Visual Cortex during Anticipation of Self-generated Visual Stimulation." Journal of Cognitive Neuroscience 26, no. 11 (November 2014): 2540–51. http://dx.doi.org/10.1162/jocn_a_00658.
Full textAbstract:
The perceived intensity of sensory stimuli is reduced when these stimuli are caused by the observer's actions. This phenomenon is traditionally explained by forward models of sensory action–outcome, which arise from motor processing. Although these forward models critically predict anticipatory modulation of sensory neural processing, neurophysiological evidence for anticipatory modulation is sparse and has not been linked to perceptual data showing sensory attenuation. By combining a psychophysical task involving contrast discrimination with source-level time–frequency analysis of MEG data, we demonstrate that the amplitude of alpha-oscillations in visual cortex is enhanced before the onset of a visual stimulus when the identity and onset of the stimulus are controlled by participants' motor actions. Critically, this prestimulus enhancement of alpha-amplitude is paralleled by psychophysical judgments of a reduced contrast for this stimulus. We suggest that alpha-oscillations in visual cortex preceding self-generated visual stimulation are a likely neurophysiological signature of motor-induced sensory anticipation and mediate sensory attenuation. We discuss our results in relation to proposals that attribute generic inhibitory functions to alpha-oscillations in prioritizing and gating sensory information via top–down control.
34
Schupp, Harald T., Junghöfer Markus, Almut I. Weike, and Alfons O. Hamm. "Emotional Facilitation of Sensory Processing in the Visual Cortex." Psychological Science 14, no. 1 (January 2003): 7–13. http://dx.doi.org/10.1111/1467-9280.01411.
Full textAbstract:
A key function of emotion is the preparation for action. However, organization of successful behavioral strategies depends on efficient stimulus encoding. The present study tested the hypothesis that perceptual encoding in the visual cortex is modulated by the emotional significance of visual stimuli. Event-related brain potentials were measured while subjects viewed pleasant, neutral, and unpleasant pictures. Early selective encoding of pleasant and unpleasant images was associated with a posterior negativity, indicating primary sources of activation in the visual cortex. The study also replicated previous findings in that affective cues also elicited enlarged late positive potentials, indexing increased stimulus relevance at higher-order stages of stimulus processing. These results support the hypothesis that sensory encoding of affective stimuli is facilitated implicitly by natural selective attention. Thus, the affect system not only modulates motor output (i.e., favoring approach or avoidance dispositions), but already operates at an early level of sensory encoding.
35
Noudoost, Behrad, Neda Nategh, Kelsey Clark, and Hossein Esteky. "Stimulus context alters neural representations of faces in inferotemporal cortex." Journal of Neurophysiology 117, no. 1 (January 1, 2017): 336–47. http://dx.doi.org/10.1152/jn.00667.2016.
Full textAbstract:
One goal of our nervous system is to form predictions about the world around us to facilitate our responses to upcoming events. One basis for such predictions could be the recently encountered visual stimuli, or the recent statistics of the visual environment. We examined the effect of recently experienced stimulus statistics on the visual representation of face stimuli by recording the responses of face-responsive neurons in the final stage of visual object recognition, the inferotemporal (IT) cortex, during blocks in which the probability of seeing a particular face was either 100% or only 12%. During the block with only face images, ∼30% of IT neurons exhibit enhanced anticipatory activity before the evoked visual response. This anticipatory modulation is followed by greater activity, broader view tuning, more distributed processing, and more reliable responses of IT neurons to the face stimuli. These changes in the visual response were sufficient to improve the ability of IT neurons to represent a variable property of the predictable face images (viewing angle), as measured by the performance of a simple linear classifier. These results demonstrate that the recent statistics of the visual environment can facilitate processing of stimulus information in the population neuronal representation. NEW & NOTEWORTHY Neurons in inferotemporal (IT) cortex anticipate the arrival of a predictable stimulus, and visual responses to an expected stimulus are more distributed throughout the population of IT neurons, providing an enhanced representation of second-order stimulus information (in this case, viewing angle). The findings reveal a potential neural basis for the behavioral benefits of contextual expectation.
36
Fahrenfort, J. J., H. S. Scholte, and V. A. F. Lamme. "Masking Disrupts Reentrant Processing in Human Visual Cortex." Journal of Cognitive Neuroscience 19, no. 9 (September 2007): 1488–97. http://dx.doi.org/10.1162/jocn.2007.19.9.1488.
Full textAbstract:
In masking, a stimulus is rendered invisible through the presentation of a second stimulus shortly after the first. Over the years, authors have typically explained masking by postulating some early disruption process. In these feedforward-type explanations, the mask somehow “catches up” with the target stimulus, disrupting its processing either through lateral or interchannel inhibition. However, studies from recent years indicate that visual perception—and most notably visual awareness itself—may depend strongly on cortico-cortical feedback connections from higher to lower visual areas. This has led some researchers to propose that masking derives its effectiveness from selectively interrupting these reentrant processes. In this experiment, we used electroencephalogram measurements to determine what happens in the human visual cortex during detection of a texture-defined square under nonmasked (seen) and masked (unseen) conditions. Electro-encephalogram derivatives that are typically associated with reentrant processing turn out to be absent in the masked condition. Moreover, extrastriate visual areas are still activated early on by both seen and unseen stimuli, as shown by scalp surface Laplacian current source-density maps. This conclusively shows that feedforward processing is preserved, even when subject performance is at chance as determined by objective measures. From these results, we conclude that masking derives its effectiveness, at least partly, from disrupting reentrant processing, thereby interfering with the neural mechanisms of figure-ground segmentation and visual awareness itself.
37
Reich, Daniel S., Ferenc Mechler, and Jonathan D. Victor. "Formal and Attribute-Specific Information in Primary Visual Cortex." Journal of Neurophysiology 85, no. 1 (January 1, 2001): 305–18. http://dx.doi.org/10.1152/jn.2001.85.1.305.
Full textAbstract:
We estimate the rates at which neurons in the primary visual cortex (V1) of anesthetized macaque monkeys transmit stimulus-related information in response to three types of visual stimulus. The stimuli—randomly modulated checkerboard patterns, stationary sinusoidal gratings, and drifting sinusoidal gratings—have very different spatiotemporal structures. We obtain the overall rate of information transmission, which we call formal information, by a direct method. We find the highest information rates in the responses of simple cells to drifting gratings (median: 10.3 bits/s, 0.92 bits/spike); responses to randomly modulated stimuli and stationary gratings transmit information at significantly lower rates. In general, simple cells transmit information at higher rates, and over a larger range, than do complex cells. Thus in the responses of V1 neurons, stimuli that are rapidly modulated do not necessarily evoke higher information rates, as might be the case with motion-sensitive neurons in area MT. By an extension of the direct method, we parse the formal information into attribute-specific components, which provide estimates of the information transmitted about contrast and spatiotemporal pattern. We find that contrast-specific information rates vary across neurons—about 0.3 to 2.1 bits/s or 0.05 to 0.22 bits/spike—but depend little on stimulus type. Spatiotemporal pattern-specific information rates, however, depend strongly on the type of stimulus and neuron (simple or complex). The remaining information rate, typically between 10 and 32% of the formal information rate for each neuron, cannot be unambiguously assigned to either contrast or spatiotemporal pattern. This indicates that some information concerning these two stimulus attributes is confounded in the responses of single neurons in V1. A model that considers a simple cell to consist of a linear spatiotemporal filter followed by a static rectifier predicts higher information rates than are found in real neurons and completely fails to replicate the performance of real cells in generating the confounded information.
38
HUGUES, ETIENNE, and JORGE V. JOSÉ. "STIMULUS COMPETITION IN ATTENTION: A NEURAL MODEL OF VISUAL CORTEX AREA V4." International Journal of Modern Physics E 17, no. 05 (May 2008): 915–23. http://dx.doi.org/10.1142/s0218301308010258.
Full textAbstract:
When a monkey is presented simultaneously two stimuli in the receptive field of a neuron in the visual cortex area V4, the neuron firing rate response is intermediate between the neuron response when both stimuli are presented alone. This phenomenon is called stimulus competition. To study its basic underlying neural mechanisms, we calculate the neuron firing rate response to different stimulus configurations. We find that stimulus competition can arise from the neuron's response properties alone, but only for a limited set of stimulus pair parameters. Furthermore, network properties may be important in modifying the inputs so that competition may occur for much wider sets of stimulus pairs.
39
Chelazzi, Leonardo, John Duncan, Earl K. Miller, and Robert Desimone. "Responses of Neurons in Inferior Temporal Cortex During Memory-Guided Visual Search." Journal of Neurophysiology 80, no. 6 (December 1, 1998): 2918–40. http://dx.doi.org/10.1152/jn.1998.80.6.2918.
Full textAbstract:
Chelazzi, Leonardo, John Duncan, Earl K. Miller, and Robert Desimone. Responses of neurons in inferior temporal cortex during memory-guided visual search. J. Neurophysiol. 80: 2918–2940, 1998. A typical scene will contain many different objects, few of which are relevant to behavior at any given moment. Thus attentional mechanisms are needed to select relevant objects for visual processing and control over behavior. We examined this role of attention in the inferior temporal cortex of macaque monkeys, using a visual search paradigm. While the monkey maintained fixation, a cue stimulus was presented at the center of gaze, followed by a blank delay period. After the delay, an array of two to five choice stimuli was presented extrafoveally, and the monkey was rewarded for detecting a target stimulus matching the cue. The behavioral response was a saccadic eye movement to the target in one version of the task and a lever release in another. The array was composed of one “good” stimulus (effective in driving the cell when presented alone) and one or more “poor” stimuli (ineffective in driving the cell when presented alone). Most cells showed higher delay activity after a good stimulus used as the cue than after a poor stimulus. The baseline activity of cells was also higher preceding a good cue, if the animal expected it to occur. This activity may depend on a top-down bias in favor of cells coding the relevant stimulus. When the choice array was presented, most cells showed suppressive interactions between the stimuli as well as strong attention effects. When the choice array was presented in the contralateral visual field, most cells initially responded the same, regardless of which stimulus was the target. However, within 150–200 ms of array onset, responses were determined by the target stimulus. If the target was the good stimulus, the response to the array became equal to the response to the good stimulus presented alone. If the target was a poor stimulus, the response approached the response to that stimulus presented alone. Thus the influence of the nontarget stimulus was eliminated. These effects occurred well in advance of the behavioral response. When the array was positioned with stimuli on opposite sides of the vertical meridian, the contralateral stimulus appeared to dominate the response, and this dominant effect could not be overcome by attention. Overall, the results support a “biased competition” model of attention, according to which 1) objects in the visual field compete for representation in the cortex, and 2) this competition is biased in favor of the behaviorally relevant object by virtue of “top-down” feedback from structures involved in working memory.
40
Railo, Henry, Niina Salminen-Vaparanta, Linda Henriksson, Antti Revonsuo, and Mika Koivisto. "Unconscious and Conscious Processing of Color Rely on Activity in Early Visual Cortex: A TMS Study." Journal of Cognitive Neuroscience 24, no. 4 (April 2012): 819–29. http://dx.doi.org/10.1162/jocn_a_00172.
Full textAbstract:
Chromatic information is processed by the visual system both at an unconscious level and at a level that results in conscious perception of color. It remains unclear whether both conscious and unconscious processing of chromatic information depend on activity in the early visual cortex or whether unconscious chromatic processing can also rely on other neural mechanisms. In this study, the contribution of early visual cortex activity to conscious and unconscious chromatic processing was studied using single-pulse TMS in three time windows 40–100 msec after stimulus onset in three conditions: conscious color recognition, forced-choice discrimination of consciously invisible color, and unconscious color priming. We found that conscious perception and both measures of unconscious processing of chromatic information depended on activity in early visual cortex 70–100 msec after stimulus presentation. Unconscious forced-choice discrimination was above chance only when participants reported perceiving some stimulus features (but not color).
41
Merchant, H., A. Battaglia-Mayer, and A. P. Georgopoulos. "Effects of Optic Flow in Motor Cortex and Area 7a." Journal of Neurophysiology 86, no. 4 (October 1, 2001): 1937–54. http://dx.doi.org/10.1152/jn.2001.86.4.1937.
Full textAbstract:
Moving visual stimuli were presented to behaving monkeys who fixated their eyes and did not move their arm. The stimuli consisted of random dots moving coherently in eight different kinds of motion (right, left, up, downward, expansion, contraction, clockwise, and counterclockwise) and were presented in 25 square patches on a liquid crystal display projection screen. Neuronal activity in the arm area of the motor cortex and area 7a was significantly influenced by the visual stimulation, as assessed using an ANOVA. The percentage of cells with a statistically significant effect of visual stimulation was 3 times greater in area 7a (370/587, 63%) than in motor cortex (148/693, 21.4%). With respect to stimulus properties, its location and kind of motion had differential effects on cell activity in the two areas. Specifically, the percentage of cells with a significant stimulus location effect was ∼2.5 times higher in area 7a (311/370, 84%) than in motor cortex (48/148, 32.4%), whereas the percentage of cells with a significant stimulus motion effect was ∼2 times higher in the motor cortex (79/148, 53.4%) than in area 7a (102/370, 27.6%). We also assessed the selectivity of responses to particular stimulus motions using a Poisson train analysis and determined the percentage of cells that showed activation in only one stimulus condition. This percentage was 2 times higher in the motor cortex (73.7%) than in area 7a (37.7%). Of all kinds of stimulus motion tested, responses to expanding optic flow were the strongest in both cortical areas. Finally, we compared the activation of motor cortical cells during visual stimulation to that observed during force exertion in a center→ out task. Of 514 cells analyzed for both the motor and visual tasks, 388 (75.5%) showed a significant relation to either or both tasks, as follows: 284/388 (73.2%) cells showed a significant relation only to the motor task, 27/388 (7%) cells showed a significant relation only to the visual task, whereas the remaining 77/388 (19.8%) cells showed significant relations to both tasks. Therefore a total of 361/514 (70.2%) cells were related to the motor task and 104/514 (20.2%) were related to the visual task. Finally, with respect to receptive fields (RFs), there was no clear visual receptive field structure in the motor cortical neuronal responses, in contrast to area 7a where RFs were present and could be modulated by the type of optic flow stimulus.
42
Bogdanova, Olena V., Volodymyr B. Bogdanov, Jean-Baptiste Durand, Yves Trotter, and Benoit R. Cottereau. "Dynamics of the straight-ahead preference in human visual cortex." Brain Structure and Function 225, no. 1 (December 2, 2019): 173–86. http://dx.doi.org/10.1007/s00429-019-01988-5.
Full textAbstract:
AbstractThe objects located straight-ahead of the body are preferentially processed by the visual system. They are more rapidly detected and evoke stronger BOLD responses in early visual areas than elements that are retinotopically identical but located at eccentric spatial positions. To characterize the dynamics of the underlying neural mechanisms, we recorded in 29 subjects the EEG responses to peripheral targets differing solely by their locations with respect to the body. Straight-ahead stimuli led to stronger responses than eccentric stimuli for several components whose latencies ranged between 70 and 350 ms after stimulus onset. The earliest effects were found at 70 ms for a component that originates from occipital areas, the contralateral P1. To determine whether the straight-ahead direction affects primary visual cortex responses, we performed an additional experiment (n = 29) specifically designed to generate two robust components, the C1 and C2, whose cortical origins are constrained within areas V1, V2 and V3. Our analyses confirmed all the results of the first experiment and also revealed that the C2 amplitude between 130 and 160 ms after stimulus onset was significantly stronger for straight-ahead stimuli. A frequency analysis of the pre-stimulus baseline revealed that gaze-driven alterations in the visual hemi-field containing the straight-ahead direction were associated with a decrease in alpha power in the contralateral hemisphere, suggesting the implication of specific neural modulations before stimulus onset. Altogether, our EEG data demonstrate that preferential responses to the straight-ahead direction can be detected in the visual cortex as early as about 70 ms after stimulus onset.
43
Lubeck, Astrid J. A., Angelique Van Ombergen, Hena Ahmad, Jelte E. Bos, Floris L. Wuyts, Adolfo M. Bronstein, and Qadeer Arshad. "Differential effect of visual motion adaption upon visual cortical excitability." Journal of Neurophysiology 117, no. 3 (March 1, 2017): 903–9. http://dx.doi.org/10.1152/jn.00655.2016.
Full textAbstract:
The objectives of this study were 1) to probe the effects of visual motion adaptation on early visual and V5/MT cortical excitability and 2) to investigate whether changes in cortical excitability following visual motion adaptation are related to the degree of visual dependency, i.e., an overreliance on visual cues compared with vestibular or proprioceptive cues. Participants were exposed to a roll motion visual stimulus before, during, and after visual motion adaptation. At these stages, 20 transcranial magnetic stimulation (TMS) pulses at phosphene threshold values were applied over early visual and V5/MT cortical areas from which the probability of eliciting a phosphene was calculated. Before and after adaptation, participants aligned the subjective visual vertical in front of the roll motion stimulus as a marker of visual dependency. During adaptation, early visual cortex excitability decreased whereas V5/MT excitability increased. After adaptation, both early visual and V5/MT excitability were increased. The roll motion-induced tilt of the subjective visual vertical (visual dependence) was not influenced by visual motion adaptation and did not correlate with phosphene threshold or visual cortex excitability. We conclude that early visual and V5/MT cortical excitability is differentially affected by visual motion adaptation. Furthermore, excitability in the early or late visual cortex is not associated with an increase in visual reliance during spatial orientation. Our findings complement earlier studies that have probed visual cortical excitability following motion adaptation and highlight the differential role of the early visual cortex and V5/MT in visual motion processing. NEW & NOTEWORTHY We examined the influence of visual motion adaptation on visual cortex excitability and found a differential effect in V1/V2 compared with V5/MT. Changes in visual excitability following motion adaptation were not related to the degree of an individual's visual dependency.
44
Rahmati, Masih, Golbarg T. Saber, and Clayton E. Curtis. "Population Dynamics of Early Visual Cortex during Working Memory." Journal of Cognitive Neuroscience 30, no. 2 (February 2018): 219–33. http://dx.doi.org/10.1162/jocn_a_01196.
Full textAbstract:
Although the content of working memory (WM) can be decoded from the spatial patterns of brain activity in early visual cortex, how populations encode WM representations remains unclear. Here, we address this limitation by using a model-based approach that reconstructs the feature encoded by population activity measured with fMRI. Using this approach, we could successfully reconstruct the locations of memory-guided saccade goals based on the pattern of activity in visual cortex during a memory delay. We could reconstruct the saccade goal even when we dissociated the visual stimulus from the saccade goal using a memory-guided antisaccade procedure. By comparing the spatiotemporal population dynamics, we find that the representations in visual cortex are stable but can also evolve from a representation of a remembered visual stimulus to a prospective goal. Moreover, because the representation of the antisaccade goal cannot be the result of bottom–up visual stimulation, it must be evoked by top–down signals presumably originating from frontal and/or parietal cortex. Indeed, we find that trial-by-trial fluctuations in delay period activity in frontal and parietal cortex correlate with the precision with which our model reconstructed the maintained saccade goal based on the pattern of activity in visual cortex. Therefore, the population dynamics in visual cortex encode WM representations, and these representations can be sculpted by top–down signals from frontal and parietal cortex.
45
Ciaramitaro, Vivian M., Giedrius T. Buračas, and Geoffrey M. Boynton. "Spatial and Cross-Modal Attention Alter Responses to Unattended Sensory Information in Early Visual and Auditory Human Cortex." Journal of Neurophysiology 98, no. 4 (October 2007): 2399–413. http://dx.doi.org/10.1152/jn.00580.2007.
Full textAbstract:
Attending to a visual or auditory stimulus often requires irrelevant information to be filtered out, both within the modality attended and in other modalities. For example, attentively listening to a phone conversation can diminish our ability to detect visual events. We used functional magnetic resonance imaging (fMRI) to examine brain responses to visual and auditory stimuli while subjects attended visual or auditory information. Although early cortical areas are traditionally considered unimodal, we found that brain responses to the same ignored information depended on the modality attended. In early visual area V1, responses to ignored visual stimuli were weaker when attending to another visual stimulus, compared with attending to an auditory stimulus. The opposite was true in more central visual area MT+, where responses to ignored visual stimuli were weaker when attending to an auditory stimulus. Furthermore, fMRI responses to the same ignored visual information depended on the location of the auditory stimulus, with stronger responses when the attended auditory stimulus shared the same side of space as the ignored visual stimulus. In early auditory cortex, responses to ignored auditory stimuli were weaker when attending a visual stimulus. A simple parameterization of our data can describe the effects of redirecting attention across space within the same modality (spatial attention) or across modalities (cross-modal attention), and the influence of spatial attention across modalities (cross-modal spatial attention). Our results suggest that the representation of unattended information depends on whether attention is directed to another stimulus in the same modality or the same region of space.
46
Richmond, B. J., and T. Sato. "Enhancement of inferior temporal neurons during visual discrimination." Journal of Neurophysiology 58, no. 6 (December 1, 1987): 1292–306. http://dx.doi.org/10.1152/jn.1987.58.6.1292.
Full textAbstract:
1. Previous results have shown that spatially directed attention enhances the stimulus-elicited responses of neurons in some areas of the brain. In the inferior temporal (IT) cortex, however, directing attention toward a stimulus mildly inhibits the responses of the neurons. Inferior temporal cortex is involved in pattern discrimination, but not spatial localization. If enhancement signifies that a neuron is participating in the function for which that part of cortex is responsible, then pattern discrimination, not spatial attention, should enhance responses of IT neurons. The influence of pattern discrimination behavior on the responses of IT neurons was therefore compared with previously reported suppressive influences of both spatial attention and the fixation point. 2. Single IT neurons were recorded from two monkeys while they performed each of five tasks. One task required the monkey to make a pattern discrimination between a bar and a square of light. In the other four tasks the same bar of light appeared, but the focus of spatial attention could differ, and the fixation point could be present or absent. Either attention to (without discrimination of) the bar stimulus or the presence of the fixation point attenuated responses slightly. These two suppressive influences produced a greater attenuation when both were present. 3. The visual conditions and motor requirements when the bar stimulus appeared in the discrimination task were identical to those of the trials in the stimulus attention task. However, one-half of the responsive neurons showed significantly stronger responses to the bar stimulus when it appeared in the discrimination task than when it appeared in the stimulus attention task. For most of these neurons, discrimination just overcame the combined effect of the two suppressive influences. For six other neurons, the response strength was significantly greater during the discrimination task than during any other task. 4. The monkeys achieved an overall correct performance rate of 90% in both the discrimination and stimulus attention tasks. To achieve this performance in the discrimination task they adopted a strategy in which they performed one trial type, bar stimulus attention trials, perfectly (100%) and the other trial type, pattern trials, relatively poorly (84% correct).(ABSTRACT TRUNCATED AT 400 WORDS)
47
Larsson, Jonas, David J. Heeger, and Michael S. Landy. "Orientation Selectivity of Motion-Boundary Responses in Human Visual Cortex." Journal of Neurophysiology 104, no. 6 (December 2010): 2940–50. http://dx.doi.org/10.1152/jn.00400.2010.
Full textAbstract:
Motion boundaries (local changes in visual motion direction) arise naturally when objects move relative to an observer. In human visual cortex, neuroimaging studies have identified a region (the kinetic occipital area [KO]) that responds more strongly to motion-boundary stimuli than to transparent-motion stimuli. However, some functional magnetic resonance imaging (fMRI) studies suggest that KO may encompass multiple visual areas and single-unit studies in macaque visual cortex have identified neurons selective for motion-boundary orientation in areas V2, V3, and V4, implying that motion-boundary selectivity may not be restricted to a single area. It is not known whether fMRI responses to motion boundaries are selective for motion-boundary orientation, as would be expected if these responses reflected the population activity of motion-boundary–selective neurons. We used an event-related fMRI adaptation protocol to measure orientation-selective responses to motion boundaries in human visual cortex. On each trial, we measured the response to a probe stimulus presented after an adapter stimulus (a vertical or horizontal motion-boundary grating). The probe stimulus was either a motion-boundary grating oriented parallel or orthogonal to the adapter stimulus or a transparent-motion stimulus. Orientation-selective adaptation for motion boundaries—smaller responses for trials in which test and adapter stimuli were parallel to each other—was observed in multiple extrastriate visual areas. The strongest adaptation, relative to the unadapted responses, was found in V3A, V3B, LO1, LO2, and V7. Most of the visual areas that exhibited orientation-selective adaptation in our data also showed response preference for motion boundaries over transparent motion, indicating that most of the human visual areas previously shown to respond to motion boundaries are also selective for motion-boundary orientation. These results suggest that neurons selective for motion-boundary orientation are distributed across multiple human visual cortical areas and argue against the existence of a single region or area specialized for motion-boundary processing.
48
Amit, Daniel J., Stefano Fusi, and Volodya Yakovlev. "Paradigmatic Working Memory (Attractor) Cell in IT Cortex." Neural Computation 9, no. 5 (July 1, 1997): 1071–92. http://dx.doi.org/10.1162/neco.1997.9.5.1071.
Full textAbstract:
We discuss paradigmatic properties of the activity of single cells comprising an attractor—a developed stable delay activity distribution. To demonstrate these properties and a methodology for measuring their values, we present a detailed account of the spike activity recorded from a single cell in the inferotemporal cortex of a monkey performing a delayed match-to-sample (DMS) task of visual images. In particular, we discuss and exemplify (1) the relation between spontaneous activity and activity immediately preceding the first stimulus in each trial during a series of DMS trials, (2) the effect on the visual response (i.e., activity during stimulation) of stimulus degradation (moving in the space of IT afferents), (3) the behavior of the delay activity (i.e., activity following visual stimulation) under stimulus degradation (attractor dynamics and the basin of attraction), and (4) the propagation of information between trials—the vehicle for the formation of (contextual) correlations by learning a fixed stimulus sequence (Miyashita, 1988). In the process of the discussion and demonstration, we expose effective tools for the identification and characterization of attractor dynamics. 1 1 A color version of this article is found on the Web at: http://www.fiz.huji.ac.il/staff/acc/faculty/damita
49
Runeson, Erik, Geoffrey M. Boynton, and Scott O. Murray. "Effects of task and attentional selection on responses in human visual cortex." Journal of Neurophysiology 109, no. 10 (May 15, 2013): 2606–17. http://dx.doi.org/10.1152/jn.00318.2012.
Full textAbstract:
Multiple visual tasks can be performed on the same visual input, with different tasks presumably engaging different neuronal populations. The modular layout of the visual system implies that specific cortical regions carry more information about certain stimulus attributes than others. Thus it is reasonable to assume that decisions during a task will be optimal if they are based on the responses of the most informative neuronal signals, which presumably originate in regions with the sharpest tuning for the relevant stimulus feature. Previous studies have supported this position. Here we present the results of two fMRI experiments that confirm these findings and expand on earlier investigations by addressing the effects of the physical properties of an attended stimulus on task-related modulations in human visual cortex. Specifically, we ask whether performing two-alternative forced choice speed- and color-discrimination tasks (and other attentional processes) can modulate neural activity independent of visual stimulation and whether the effect of spatial attention depends on which task is being performed. The results indicate that 1) when stimulation and spatial attention are constant, responses in V4 and MT+ depend on the task being performed and are independent of the tested physical properties of the selected stimulus, 2) this task-dependent modulation might require a stimulus—task-specific preparatory mechanisms alone are not sufficient to drive responses, and 3) independent of which task is being performed, spatial attention adds a baseline shift to responses in MT+ and V4 when a stimulus is present.
50
de Haas, Benjamin, D. Samuel Schwarzkopf, Maren Urner, and Geraint Rees. "Auditory modulation of visual stimulus encoding in human retinotopic cortex." NeuroImage 70 (April 2013): 258–67. http://dx.doi.org/10.1016/j.neuroimage.2012.12.061.
Full text