scholarly journals Task context modulates feature-selective responses in area V4

2019 ◽  
Author(s):  
Dina V. Popovkina ◽  
Anitha Pasupathy
Keyword(s):  
Discrimination Task ◽  
Feature Space ◽  
Task Engagement ◽  
Task Context ◽  
Area V4 ◽  
Neuronal Tuning ◽  
Partial View ◽  
Color Combinations ◽  
V4 Neurons ◽  
Passive Fixation

ABSTRACTFeature selectivity of neuronal responses in primate visual cortex is typically measured while animals fixate a small dot on the screen and a stimulus is presented in the near-periphery. This paradigm allows the efficient exploration of feature space, but it provides only a partial view of selectivity by failing to characterize how cognitive factors influence neuronal tuning. Here we focus on primate area V4, known to be influenced by cognitive processes, and ask how neuronal tuning is modulated by task engagement. We compared the tuning for shape and color in 83 well-isolated V4 neurons measured during passive fixation and during active engagement in a shape discrimination task. In both tasks, animals saw the same set of objects—shape x color combinations—but while neither stimulus feature was relevant during the fixation task, shape identity was relevant for behavior during the discrimination task. Consistent with attentional studies, V4 responses during the discrimination task showed a stimulus-independent gain scaling relative to passive fixation, but this was only in a minority of neurons (21/83). For the rest (62/83), response modulations during discrimination depended on stimulus identity: on stimulus shape in neurons more strongly tuned to shape, and on color in neurons more strongly tuned to color. Overall, this resulted in broader tuning for stimulus color, but not shape, during active task engagement. These results suggest that task context can influence the shape and color selectivity of V4 neurons, and in some neurons this effect is consistent with a change in the width of feature tuning.

Differential Temporal Storage Capacity in the Baseline Activity of Neurons in Macaque Frontal Eye Field and Area V4

2010 ◽  
Vol 103 (5) ◽  
pp. 2433-2445 ◽  
Author(s):  
Tadashi Ogawa ◽  
Hidehiko Komatsu
Keyword(s):  
Neuronal Activity ◽  
Storage Capacity ◽  
Discharge Rate ◽  
Time Lag ◽  
Temporal Correlation ◽  
Frontal Eye Field ◽  
Area V4 ◽  
Baseline Activity ◽  
Eye Field ◽  
V4 Neurons

Previous studies have suggested that spontaneous fluctuations in neuronal activity reflect intrinsic functional brain architecture. Inspired by these findings, we analyzed baseline neuronal activity in the monkey frontal eye field (FEF; a visuomotor area) and area V4 (a visual area) during the fixation period of a cognitive behavioral task in the absence of any task-specific stimuli or behaviors. Specifically, we examined the temporal storage capacity of the instantaneous discharge rate in FEF and V4 neurons by calculating the correlation of the spike count in a bin with that in another bin during the baseline activity of a trial. We found that most FEF neurons fired significantly more (or less) in one bin if they fired more (or less) in another bin within a trial, even when these two time bins were separated by hundreds of milliseconds. By contrast, similar long time-lag correlations were observed in only a small fraction of V4 neurons, indicating that temporal correlations were considerably stronger in FEF compared with those in V4 neurons. Additional analyses revealed that the findings were not attributable to other task-related variables or ongoing behavioral performance, suggesting that the differences in temporal correlation strength reflect differences in intrinsic structural and functional architecture between visual and visuomotor areas. Thus FEF neurons probably play a greater role than V4 neurons in neural circuits responsible for temporal storage in activity.

scholarly journals Changes in the Response Rate and Response Variability of Area V4 Neurons During the Preparation of Saccadic Eye Movements

2010 ◽  
Vol 103 (3) ◽  
pp. 1171-1178 ◽  
Author(s):  
Nicholas A. Steinmetz ◽  
Tirin Moore
Keyword(s):  
Eye Movements ◽  
Reaction Time ◽  
Firing Rate ◽  
Response Rate ◽  
Saccadic Eye Movements ◽  
Response Variability ◽  
Area V4 ◽  
The Mean ◽  
V4 Neurons ◽  
Saccade Preparation

The visually driven responses of macaque area V4 neurons are modulated during the preparation of saccadic eye movements, but the relationship between presaccadic modulation in area V4 and saccade preparation is poorly understood. Recent neurophysiological studies suggest that the variability across trials of spiking responses provides a more reliable signature of motor preparation than mean firing rate across trials. We compared the dynamics of the response rate and the variability in the rate across trials for area V4 neurons during the preparation of visually guided saccades. As in previous reports, we found that the mean firing rate of V4 neurons was enhanced when saccades were prepared to stimuli within a neuron's receptive field (RF) in comparison with saccades to a non-RF location. Further, we found robust decreases in response variability prior to saccades and found that these decreases predicted saccadic reaction times for saccades both to RF and non-RF stimuli. Importantly, response variability predicted reaction time whether or not there were any accompanying changes in mean firing rate. In addition to predicting saccade direction, the mean firing rate could also predict reaction time, but only for saccades directed to the RF stimuli. These results demonstrate that response variability of area V4 neurons, like mean response rate, provides a signature of saccade preparation. However, the two signatures reflect complementary aspects of that preparation.

Quantitative Characterization of Disparity Tuning in Ventral Pathway Area V4

2005 ◽  
Vol 94 (4) ◽  
pp. 2726-2737 ◽  
Author(s):  
David A. Hinkle ◽  
Charles E. Connor
Keyword(s):  
Binocular Disparity ◽  
Orientation Tuning ◽  
Quantitative Characterization ◽  
Object Processing ◽  
Gaussian Functions ◽  
Area V4 ◽  
Ventral Pathway ◽  
Object Parts ◽  
V4 Neurons

We performed a quantitative characterization of binocular disparity-tuning functions in the ventral (object-processing) pathway of the macaque visual cortex. We measured responses of 452 area V4 neurons to stimuli with disparities ranging from −1.0 to +1.0°. Asymmetric Gaussian functions fit the raw data best (median R = 0.90), capturing both the modal components (local peaks in the −1.0 to +1.0° range) and the monotonic components (linear or sigmoidal dependency on disparity) of the tuning patterns. Values derived from the asymmetric Gaussian fits were used to characterize neurons on a modal × monotonic tuning domain. Points along the modal tuning axis correspond to classic tuned excitatory and inhibitory patterns; points along the monotonic axis correspond to classic near and far patterns. The distribution on this domain was continuous, with the majority of neurons exhibiting a mixed modal/monotonic tuning pattern. The distribution in the modal dimension was shifted toward excitatory patterns, consistent with previous results in other areas. The distribution in the monotonic dimension was shifted toward tuning for crossed disparities (corresponding to stimuli nearer than the fixation plane). This could reflect a perceptual emphasis on objects or object parts closer to the observer. We also found that disparity-tuning strength was positively correlated with orientation-tuning strength and color-tuning strength, and negatively correlated with receptive field eccentricity.

scholarly journals Receptive field focus of visual area V4 neurons determines responses to illusory surfaces

2013 ◽  
Vol 110 (42) ◽  
pp. 17095-17100 ◽  
Author(s):  
M. A. Cox ◽  
M. C. Schmid ◽  
A. J. Peters ◽  
R. C. Saunders ◽  
D. A. Leopold ◽  
...  
Keyword(s):  
Receptive Field ◽  
Visual Area ◽  
Area V4 ◽  
Visual Area V4 ◽  
V4 Neurons

scholarly journals Dynamic representation of partially occluded objects in primate prefrontal and visual cortex

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Amber M Fyall ◽  
Yasmine El-Shamayleh ◽  
Hannah Choi ◽  
Eric Shea-Brown ◽  
Anitha Pasupathy
Keyword(s):  
Visual Cortex ◽  
Response Dynamics ◽  
Dynamic Interactions ◽  
Area V4 ◽  
Dynamic Representation ◽  
Occluded Objects ◽  
Response Onset ◽  
Shape Selective ◽  
Partially Occluded ◽  
V4 Neurons

Successful recognition of partially occluded objects is presumed to involve dynamic interactions between brain areas responsible for vision and cognition, but neurophysiological evidence for the involvement of feedback signals is lacking. Here, we demonstrate that neurons in the ventrolateral prefrontal cortex (vlPFC) of monkeys performing a shape discrimination task respond more strongly to occluded than unoccluded stimuli. In contrast, neurons in visual area V4 respond more strongly to unoccluded stimuli. Analyses of V4 response dynamics reveal that many neurons exhibit two transient response peaks, the second of which emerges after vlPFC response onset and displays stronger selectivity for occluded shapes. We replicate these findings using a model of V4/vlPFC interactions in which occlusion-sensitive vlPFC neurons feed back to shape-selective V4 neurons, thereby enhancing V4 responses and selectivity to occluded shapes. These results reveal how signals from frontal and visual cortex could interact to facilitate object recognition under occlusion.

scholarly journals Pooled, but not single-neuron, responses in macaque V4 represent a solution to the stereo correspondence problem

2016 ◽  
Vol 115 (4) ◽  
pp. 1917-1931 ◽  
Author(s):  
Mohammad Abdolrahmani (ﻣﺤﻤﺪ ﻋﺒﺪاﻟﺮﺣﻤﻨﯽ) ◽  
Takahiro Doi (土井隆弘) ◽  
Hiroshi M. Shiozaki (塩崎博史) ◽  
Ichiro Fujita (藤田一郎)
Keyword(s):  
Single Neuron ◽  
Temporal Cortex ◽  
Inferior Temporal Cortex ◽  
Correspondence Problem ◽  
Tuning Curves ◽  
Area V4 ◽  
Random Dot Stereograms ◽  
Left And Right ◽  
V4 Neurons ◽  
Psychophysical Studies

Binocular disparity is an important cue for depth perception. To correctly represent disparity, neurons must find corresponding visual features between the left- and right-eye images. The visual pathway ascending from V1 to inferior temporal cortex solves the correspondence problem. An intermediate area, V4, has been proposed to be a critical stage in the correspondence process. However, the distinction between V1 and V4 is unclear, because accumulating evidence suggests that the process begins within V1. In this article, we report that the pooled responses in macaque V4, but not responses of individual neurons, represent a solution to the correspondence problem. We recorded single-unit responses of V4 neurons to random-dot stereograms of varying degrees of anticorrelation. To achieve gradual anticorrelation, we reversed the contrast of an increasing proportion of dots as in our previous psychophysical studies, which predicted that the neural correlates of the solution to correspondence problem should gradually eliminate their disparity modulation as the level of anticorrelation increases. Inconsistent with this prediction, the tuning amplitudes of individual V4 neurons quickly decreased to a nonzero baseline with small anticorrelation. By contrast, the shapes of individual tuning curves changed more gradually so that the amplitude of population-pooled responses gradually decreased toward zero over the entire range of graded anticorrelation. We explain these results by combining multiple energy-model subunits. From a comparison with the population-pooled responses in V1, we suggest that disparity representation in V4 is distinctly advanced from that in V1. Population readout of V4 responses provides disparity information consistent with the correspondence solution.

Focal attention produces spatially selective processing in visual cortical areas V1, V2, and V4 in the presence of competing stimuli

1993 ◽  
Vol 70 (3) ◽  
pp. 909-919 ◽  
Author(s):  
B. C. Motter
Keyword(s):  
Receptive Field ◽  
Stimulus Presentation ◽  
Spatial Location ◽  
Differential Sensitivity ◽  
Orientation Tuning ◽  
Area V4 ◽  
Focal Attention ◽  
V4 Neurons ◽  
Visual Cortical ◽  
Competing Stimuli

1. The activity of single neurons was recorded in Macaca mulatta monkeys while they performed tasks requiring them to select a cued stimulus from an array of three to eight stimuli and report the orientation of that stimulus. Stimuli were presented in a circular array centered on the fixation target and scaled to place a single stimulus element within the receptive field of the neuron under study. The timing of the cuing event permitted the directing of visual attention to the spatial location of the correct stimulus before its presentation. 2. The effects of focal attention were examined in cortical visual areas V1, V2, and V4, where a total of 672 neurons were isolated with complete studies obtained for 94 V1, 74 V2, and 74 V4 neurons with receptive-field center eccentricities in the range 1.8-8 degrees. Under certain conditions, directed focal attention results in changes in the response of V1, V2, and V4 neurons to otherwise identical stimuli at spatially specific locations. 3. More than one-third of the neurons in each area displayed differential sensitivity when attention was directed toward versus away from the spatial location of the receptive field just before and during stimulus presentation. Both relative increases and decreases in neural activity were observed in association with attention directed at receptive-field stimuli. 4. The presence of multiple competing stimuli in the visual field was a major factor determining the presence or absence of differential sensitivity. About two-thirds of the neurons that were differentially sensitive to the attending condition in the presence of competing stimuli were not differentially sensitive when single stimuli were presented in control studies. For V1 and V2 neurons the presence of only a few (3-4) competing stimuli was sufficient for a majority of the neurons studied; a majority of the V4 neurons required six to eight stimuli in the array before significant differences between attending conditions occurred. 5. For V1 and V2 neurons the neuronal sensitivity differences between attending conditions were observed primarily at or near the peak of the orientation tuning sensitivity for each neuron; the differences were evident over a broader range of orientations in V4 neurons. 6. In conclusion, neural correlates of focal attentive processes can be observed in visual cortical processing in areas V1 and V2 as well as area V4 under conditions that require stimulus feature analysis and selective spatial processing within a field of competing stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Representation of Stereoscopic Depth Based on Relative Disparity in Macaque Area V4

2007 ◽  
Vol 98 (1) ◽  
pp. 241-252 ◽  
Author(s):  
Kazumasa Umeda ◽  
Seiji Tanabe ◽  
Ichiro Fujita
Keyword(s):  
Stereoscopic Vision ◽  
Stereoscopic Depth ◽  
Common Mechanism ◽  
Tuning Curves ◽  
Area V4 ◽  
Neural Representations ◽  
Area V2 ◽  
Random Dot Stereogram ◽  
V4 Neurons ◽  
Background Feature

Stereoscopic vision is characterized by greater visual acuity when a background feature serves as a reference. When a reference is present, the perceived depth of an object is predominantly dependent on this reference. Neural representations of stereoscopic depth are expected to have a relative frame of reference. The conversion of absolute disparity encoded in area V1 to relative disparity begins in area V2, although the information encoded in this area appears to be insufficient for stereopsis. This study examines whether relative disparity is encoded in a higher cortical area. We recorded the responses of V4 neurons from macaque monkeys to various combinations of the absolute disparities of two features: the center patch and surrounding annulus of a dynamic random-dot stereogram. We analyzed the effects of the disparity of the surrounding annulus on the tuning for the disparity of the center patch; the tuning curves of relative-disparity–selective neurons for disparities of the center patch should shift with changes in the disparity of the surrounding annulus. Most V4 tuning curves exhibited significant shifts. The magnitudes of the shifts were larger than those reported for V2 neurons and smaller than that expected for an ideal relative-disparity–selective cell. No correlation was found between the shift magnitude and the degree of size suppression, suggesting that the two phenomena are not the result of a common mechanism. Our results suggest that the coding of relative disparity advances as information flows along the cortical pathway that includes areas V2 and V4.

Disparity-Selective Neurons in Area V4 of Macaque Monkeys

2002 ◽  
Vol 87 (4) ◽  
pp. 1960-1973 ◽  
Author(s):  
Masayuki Watanabe ◽  
Hiroki Tanaka ◽  
Takanori Uka ◽  
Ichiro Fujita
Keyword(s):  
Receptive Field ◽  
Binocular Disparity ◽  
Temporal Cortex ◽  
Intermediate Stage ◽  
Visual Pathway ◽  
Inferior Temporal Cortex ◽  
Tuning Curves ◽  
Area V4 ◽  
Ventral Visual Pathway ◽  
V4 Neurons

Area V4 is an intermediate stage of the ventral visual pathway providing major input to the final stages in the inferior temporal cortex (IT). This pathway is involved in the processing of shape, color, and texture. IT neurons are also sensitive to horizontal binocular disparity, suggesting that binocular disparity is processed along the ventral visual pathway. In the present study, we examined the processing of binocular disparity information by V4 neurons. We recorded responses of V4 neurons to binocularly disparate stimuli. A population of V4 neurons modified their responses according to changes of stimulus disparity; neither monocular responses nor eye movements could account for this modulation. Disparity-tuning curves were similar for different locations within a neuron's receptive field. Neighboring neurons recorded using a single electrode displayed similar disparity-tuning properties. These findings indicate that a population of V4 neurons is selective for binocular disparity, invariant for the position of the stimulus within the receptive field. The finding that V4 neurons with similar disparity selectivity are clustered suggests the existence of functional modules for disparity processing in V4.

Disparity-Tuning Characteristics of Neuronal Responses to Dynamic Random-Dot Stereograms in Macaque Visual Area V4

2005 ◽  
Vol 94 (4) ◽  
pp. 2683-2699 ◽  
Author(s):  
Seiji Tanabe ◽  
Takahiro Doi ◽  
Kazumasa Umeda ◽  
Ichiro Fujita
Keyword(s):  
Striate Cortex ◽  
Broad Band ◽  
Structural Features ◽  
Stereoscopic Depth ◽  
Tuning Curves ◽  
Gabor Function ◽  
Area V4 ◽  
Random Dot Stereograms ◽  
Response Preferences ◽  
V4 Neurons

Stereo processing begins in the striate cortex and involves several extrastriate visual areas. We quantitatively analyzed the disparity-tuning characteristics of neurons in area V4 of awake, fixating monkeys. Approximately half of the analyzed V4 cells were tuned for horizontal binocular disparities embedded in dynamic random-dot stereograms (RDSs). Their response preferences were strongly biased for crossed disparities. To characterize the disparity-tuning profile, we fitted a Gabor function to the disparity-tuning data. The distribution of V4 cells showed a single dense cluster in a joint parameter space of the center and the phase parameters of the fitted Gabor function; most V4 neurons were maximally sensitive to fine stereoscopic depth increments near zero disparity. Comparing single-cell responses with background multiunit responses at the same sites showed that disparity-sensitive cells were clustered within V4 and that nearby cells possessed similar preferred disparities. Consistent with a recent report by Hegdé and Van Essen, the disparity tuning for an RDS drastically differed from that for a solid-figure stereogram (SFS). Disparity-tuning curves were generally broader for SFSs than for RDSs, and there was no correlation between the fitted Gabor functions' amplitudes, widths, or peaks for the two types of stereograms. The differences were partially attributable to shifts in the monocular images of an SFS. Our results suggest that the representation of stereoscopic depth in V4 is suited for detecting fine structural features protruding from a background. The representation is not generic and differs when the stimulus is broad-band noise or a solid figure.

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