scholarly journals Temporally evolving gain mechanisms of attention in macaque area V4

2017 ◽  
Vol 118 (2) ◽  
pp. 964-985 ◽  
Author(s):  
Ilaria Sani ◽  
Elisa Santandrea ◽  
Maria Concetta Morrone ◽  
Leonardo Chelazzi
Keyword(s):  
Visual Processing ◽  
Temporal Dynamics ◽  
Luminance Contrast ◽  
Response Functions ◽  
Fundamental Factor ◽  
Area V4 ◽  
V4 Neurons ◽  
Contrast Response

We offer an innovative perspective on the interplay between attention and luminance contrast in macaque area V4, one in which time becomes a fundamental factor. We place emphasis on the temporal dynamics of attentional effects, pioneering the notion that attention modulates contrast response functions of V4 neurons via the sequential engagement of distinct gain mechanisms. These findings advance understanding of attentional influences on visual processing and help reconcile divergent results in the literature.

Effects of Spatial Attention on Contrast Response Functions in Macaque Area V4

2006 ◽  
Vol 96 (1) ◽  
pp. 40-54 ◽  
Author(s):  
Tori Williford ◽  
John H. R. Maunsell
Keyword(s):  
Spatial Attention ◽  
Response Function ◽  
Response Functions ◽  
Stimulus Response ◽  
Area V4 ◽  
Leftward Shift ◽  
Contrast Response Function ◽  
Proportional Increase ◽  
V4 Neurons ◽  
Contrast Response

Previous single-unit studies of visual cortex have reported that spatial attention modulates responses to different orientations and directions proportionally, such that it does not change the width of tuning functions for these properties. Other studies have suggested that spatial attention causes a leftward shift in contrast response functions, such that its effects on responses to stimuli of different contrasts are not proportional. We have further explored the effects of attention on stimulus-response functions by measuring the responses of 131 individual V4 neurons in two monkeys while they did a task that controlled their spatial attention. Each neuron was tested with a set of stimuli that spanned complete ranges of orientation and contrast during different states of attention. Consistent with earlier reports, attention scaled responses to preferred and nonpreferred orientations proportionally. However, we did not find compelling evidence that the effects were best described by a leftward shift of the contrast response function. The modulation of neuronal responses by attention was well described by either a leftward shift or proportional scaling of the contrast response function. Consideration of differences in experimental design and analysis that may have contributed to this discrepancy suggests that it was premature to exclude a proportional scaling of responses to different contrasts by attention in favor of a leftward shift of contrast response functions. The current results reopen the possibility that the effects of attention on stimulus-response functions are well described by a single proportional increase in a neuron's response to all stimuli.

scholarly journals Can Contrast-Response Functions Indicate Visual Processing Levels?

Vision ◽  
2018 ◽  
Vol 2 (1) ◽  
pp. 14 ◽  
Author(s):  
Bruno Breitmeyer ◽  
Srimant Tripathy ◽  
James Brown
Keyword(s):  
Visual Processing ◽  
Response Functions ◽  
Contrast Response

scholarly journals Demands of visual processing hierarchy shape laminar compartmentalization of attention modulation of luminance contrast in area V4

2021 ◽  
Author(s):  
Xiang Wang ◽  
Anirvan S. Nandy ◽  
Monika P. Jadi
Keyword(s):  
Visual Processing ◽  
Luminance Contrast ◽  
Cortical Layer ◽  
Inhibitory Neurons ◽  
Spatial Integration ◽  
Low Contrast ◽  
Area V4 ◽  
Visual Areas ◽  
Excitatory Neurons ◽  
Contrast Information

ABSTRACTContrast is a key feature of the visual scene that aids object recognition. Attention has been shown to selectively enhance the responses to low contrast stimuli in visual area V4, a critical hub that sends projections both up and down the visual hierarchy. Veridical encoding of contrast information is a key computation in early visual areas, while later stages encode higher level features that benefit from improved sensitivity to low contrast. How area V4 meets these distinct information processing demands in the attentive state is not known. We found that attentional modulation of contrast responses in area V4 is cortical layer and cell-class specific. Putative excitatory neurons in the superficial output layers that project to higher areas show enhanced boosting of low contrast information. On the other hand, putative excitatory neurons of deep output layers that project to early visual areas exhibit contrast-independent scaling. Computational modeling revealed that such layer-wise differences may result from variations in spatial integration extent of inhibitory neurons. These findings reveal that the nature of interactions between attention and contrast in V4 is highly compartmentalized, in alignment with the demands of the visual processing hierarchy.

Temporal dynamics of 2D and 3D shape representation in macaque visual area V4

2006 ◽  
Vol 23 (5) ◽  
pp. 749-763 ◽  
Author(s):  
JAY HEGDÉ ◽  
DAVID C. VAN ESSEN
Keyword(s):  
Temporal Dynamics ◽  
Shape Representation ◽  
Macaque Monkey ◽  
Large Stimulus ◽  
3D Shape ◽  
Area V4 ◽  
Single Animal ◽  
Distributed Process ◽  
V4 Neurons ◽  
2D And 3D

We studied the temporal dynamics of shape representation in area V4 of the alert macaque monkey. Analyses were based on two large stimulus sets, one equivalent to the 2D shape stimuli used in a previous study of V2, and the other a set of stereoscopic 3D shape stimuli. As in V2, we found that information conveyed by individual V4 neurons about the stimuli tended to be maximal during the initial transient response and generally lower, albeit statistically significant, afterwards. The population response was substantially correlated from one stimulus to the next during the transients, and decorrelated as responses decayed. V4 responses showed significantly longer latencies than in V2, especially for the 3D stimulus set. Recordings from area V1 in a single animal revealed temporal dynamic patterns in response to the 2D shape stimuli that were largely similar to those in V2 and V4. Together with earlier results, these findings provide evidence for a distributed process of coarse-to-fine representation of shape stimuli in the visual cortex.

scholarly journals Contrast Sensitivity Is Enhanced by Expansive Nonlinear Processing in the Lateral Geniculate Nucleus

2008 ◽  
Vol 99 (1) ◽  
pp. 367-372 ◽  
Author(s):  
Thang Duong ◽  
Ralph D. Freeman
Keyword(s):  
Visual Cortex ◽  
Lateral Geniculate Nucleus ◽  
Visual Processing ◽  
Linear Prediction ◽  
Visual Pathway ◽  
Low Contrast ◽  
Response Data ◽  
Lateral Geniculate ◽  
Nonlinear Processing ◽  
Contrast Response

The firing rates of neurons in the central visual pathway vary with stimulus strength, but not necessarily in a linear manner. In the contrast domain, the neural response function for cells in the primary visual cortex is characterized by expansive and compressive nonlinearities at low and high contrasts, respectively. A compressive nonlinearity at high contrast is also found for early visual pathway neurons in the lateral geniculate nucleus (LGN). This mechanism affects processing in the visual cortex. A fundamentally related issue is the possibility of an expansive nonlinearity at low contrast in LGN. To examine this possibility, we have obtained contrast–response data for a population of LGN neurons. We find for most cells that the best-fit function requires an expansive component. Additionally, we have measured the responses of LGN neurons to m-sequence white noise and examined the static relationship between a linear prediction and actual spike rate. We find that this static relationship is well fit by an expansive nonlinear power law with average exponent of 1.58. These results demonstrate that neurons in early visual pathways exhibit expansive nonlinear responses at low contrasts. Although this thalamic expansive nonlinearity has been largely ignored in models of early visual processing, it may have important consequences because it potentially affects the interpretation of a variety of visual functions.

Processing of Kinetic Boundaries in Macaque V4

2006 ◽  
Vol 95 (3) ◽  
pp. 1864-1880 ◽  
Author(s):  
Santosh G. Mysore ◽  
Rufin Vogels ◽  
Steve E. Raiguel ◽  
Guy A. Orban
Keyword(s):  
Relative Motion ◽  
Receptive Fields ◽  
Shape Selectivity ◽  
Luminance Contrast ◽  
Motion Cues ◽  
Form Processing ◽  
Similar Shape ◽  
Shape Selective ◽  
Sizeable Fraction ◽  
V4 Neurons

We used gratings and shapes defined by relative motion to study selectivity for static kinetic boundaries in macaque V4 neurons. Kinetic gratings were generated by random pixels moving in opposite directions in the neighboring bars, either parallel to the orientation of the boundary (parallel kinetic grating) or perpendicular to the boundary (orthogonal kinetic grating). Neurons were also tested with static, luminance defined gratings to establish cue invariance. In addition, we used eight shapes defined either by relative motion or by luminance contrast, as used previously to test cue invariance in the infero-temporal (IT) cortex. A sizeable fraction (10–20%) of the V4 neurons responded selectively to kinetic patterns. Most neurons selective for kinetic contours had receptive fields (RFs) within the central 10° of the visual field. Neurons selective for the orientation of kinetic gratings were defined as having similar orientation preferences for the two types of kinetic gratings, and the vast majority of these neurons also retained the same orientation preference for luminance defined gratings. Also, kinetic shape selective neurons had similar shape preferences when the shape was defined by relative motion or by luminance contrast, showing a cue-invariant form processing in V4. Although shape selectivity was weaker in V4 than what has been reported in the IT cortex, cue invariance was similar in the two areas, suggesting that invariance for luminance and motion cues of IT originates in V4. The neurons selective for kinetic patterns tended to be clustered within dorsal V4.

scholarly journals Distinguishing Hemodynamics from Function in the Human LGN Using a Temporal Response Model

Vision ◽  
2019 ◽  
Vol 3 (2) ◽  
pp. 27 ◽  
Author(s):  
Kevin DeSimone ◽  
Keith A. Schneider
Keyword(s):  
Receptive Field ◽  
Visual Processing ◽  
Field Model ◽  
Ventral Surface ◽  
Impulse Response Functions ◽  
Response Model ◽  
Response Functions ◽  
Temporal Response ◽  
Point Of Entry ◽  
Temporal Properties

We developed a temporal population receptive field model to differentiate the neural and hemodynamic response functions (HRF) in the human lateral geniculate nucleus (LGN). The HRF in the human LGN is dominated by the richly vascularized hilum, a structure that serves as a point of entry for blood vessels entering the LGN and supplying the substrates of central vision. The location of the hilum along the ventral surface of the LGN and the resulting gradient in the amplitude of the HRF across the extent of the LGN have made it difficult to segment the human LGN into its more interesting magnocellular and parvocellular regions that represent two distinct visual processing streams. Here, we show that an intrinsic clustering of the LGN responses to a variety of visual inputs reveals the hilum, and further, that this clustering is dominated by the amplitude of the HRF. We introduced a temporal population receptive field model that includes separate sustained and transient temporal impulse response functions that vary on a much short timescale than the HRF. When we account for the HRF amplitude, we demonstrate that this temporal response model is able to functionally segregate the residual responses according to their temporal properties.

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.

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