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 Shape encoding consistency across colors in primate V4

2012 ◽  
Vol 108 (5) ◽  
pp. 1299-1308 ◽  
Author(s):  
Brittany N. Bushnell ◽  
Anitha Pasupathy
Keyword(s):  
Correlation Coefficients ◽  
Shape Selectivity ◽  
Shape Information ◽  
Area V4 ◽  
Neuronal Populations ◽  
Shape Encoding ◽  
Shape Selective ◽  
Different Shapes ◽  
V4 Neurons ◽  
Response Consistency

Neurons in primate cortical area V4 are sensitive to the form and color of visual stimuli. To determine whether form selectivity remains consistent across colors, we studied the responses of single V4 neurons in awake monkeys to a set of two-dimensional shapes presented in two different colors. For each neuron, we chose two colors that were visually distinct and that evoked reliable and different responses. Across neurons, the correlation coefficient between responses in the two colors ranged from −0.03 to 0.93 (median 0.54). Neurons with highly consistent shape responses, i.e., high correlation coefficients, showed greater dispersion in their responses to the different shapes, i.e., greater shape selectivity, and also tended to have less eccentric receptive field locations; among shape-selective neurons, shape consistency ranged from 0.16 to 0.93 (median 0.63). Consistency of shape responses was independent of the physical difference between the stimulus colors used and the strength of neuronal color tuning. Finally, we found that our measurement of shape response consistency was strongly influenced by the number of stimulus repeats: consistency estimates based on fewer than 10 repeats were substantially underestimated. In conclusion, our results suggest that neurons that are likely to contribute to shape perception and discrimination exhibit shape responses that are largely consistent across colors, facilitating the use of simpler algorithms for decoding shape information from V4 neuronal populations.

scholarly journals Spectral receptive fields do not explain tuning for boundary curvature in V4

2014 ◽  
Vol 112 (9) ◽  
pp. 2114-2122 ◽  
Author(s):  
Timothy D. Oleskiw ◽  
Anitha Pasupathy ◽  
Wyeth Bair
Keyword(s):  
Shape Representation ◽  
Angular Position ◽  
Receptive Fields ◽  
Shape Selectivity ◽  
Neural Representation ◽  
Phase Information ◽  
Area V4 ◽  
Visual Cortical Area ◽  
V4 Neurons ◽  
Contour Curvature

The midlevel visual cortical area V4 in the primate is thought to be critical for the neural representation of visual shape. Several studies agree that V4 neurons respond to contour features, e.g., convexities and concavities along a shape boundary, that are more complex than the oriented segments encoded by neurons in the primary visual cortex. Here we compare two distinct approaches to modeling V4 shape selectivity: one based on a spectral receptive field (SRF) map in the orientation and spatial frequency domain and the other based on a map in an object-centered angular position and contour curvature space. We test the ability of these two characterizations to account for the responses of V4 neurons to a set of parametrically designed two-dimensional shapes recorded previously in the awake macaque. We report two lines of evidence suggesting that the SRF model does not capture the contour sensitivity of V4 neurons. First, the SRF model discards spatial phase information, which is inconsistent with the neuronal data. Second, the amount of variance explained by the SRF model was significantly less than that explained by the contour curvature model. Notably, cells best fit by the curvature model were poorly fit by the SRF model, the latter being appropriate for a subset of V4 neurons that appear to be orientation tuned. These limitations of the SRF model suggest that a full understanding of midlevel shape representation requires more complicated models that preserve phase information and perhaps deal with object segmentation.

scholarly journals Maximizing sinusoidal channels of HZSM-5 for high shape-selectivity to p-xylene

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Chuanfu Wang ◽  
Lei Zhang ◽  
Xin Huang ◽  
Yufei Zhu ◽  
Gang (Kevin) Li ◽  
...  
Keyword(s):  
High Activity ◽  
Chemical Industry ◽  
Chemical Separation ◽  
Shape Selectivity ◽  
Toluene Alkylation ◽  
Shape Selective ◽  
Toluene Methylation ◽  
Selective Catalysis ◽  
The Cost ◽  
Very High

Abstract The shape-selective catalysis enabled by zeolite micropore’s molecular-sized sieving is an efficient way to reduce the cost of chemical separation in the chemical industry. Although well studied since its discovery, HZSM-5′s shape-selective capability has never been fully exploited due to the co-existence of its different-sized straight channels and sinusoidal channels, which makes the shape-selective p-xylene production from toluene alkylation with the least m-xylene and o-xylene continue to be one of the few industrial challenges in the chemical industry. Rather than modifications which promote zeolite shape-selectivity at the cost of stability and reactivity loss, here inverse Al zoned HZSM-5 with sinusoidal channels predominantly opened to their external surfaces is constructed to maximize the shape-selectivity of HZSM-5 sinusoidal channels and reach > 99 % p-xylene selectivity, while keeping a very high activity and good stability ( > 220 h) in toluene methylation reactions. The strategy shows good prospects for shape-selective control of molecules with tiny differences in size.

Psychophysical evidence for interactions between visual motion and form processing at the level of motion integrating receptive fields

2012 ◽  
Vol 50 (1) ◽  
pp. 153-159 ◽  
Author(s):  
George Mather ◽  
Andrea Pavan ◽  
Rosilari M. Bellacosa ◽  
Clara Casco
Keyword(s):  
Visual Motion ◽  
Receptive Fields ◽  
Form Processing

Shape-selective alkylation of biphenyl over mordenites: effects of dealumination on shape-selectivity and coke deposition

1994 ◽  
Vol 26 (1-2) ◽  
pp. 181-187 ◽  
Author(s):  
Y. Sugi ◽  
T. Matsuzaki ◽  
T. Hanaoka ◽  
Y. Kubota ◽  
J. -H. Kim ◽  
...  
Keyword(s):  
Shape Selectivity ◽  
Coke Deposition ◽  
Shape Selective ◽  
Selective Alkylation

The response dynamics of primate visual cortical neurons to simulated optical blur

2009 ◽  
Vol 26 (4) ◽  
pp. 411-420 ◽  
Author(s):  
MICHAEL L. RISNER ◽  
TIMOTHY J. GAWNE
Keyword(s):  
Cortical Neurons ◽  
Receptive Fields ◽  
Luminance Contrast ◽  
Form Perception ◽  
Response Dynamics ◽  
V1 Neurons ◽  
Spatial Frequencies ◽  
Wide Range ◽  
Optical Blur ◽  
Visual Cortical

AbstractNeurons in visual cortical area V1 typically respond well to lines or edges of specific orientations. There have been many studies investigating how the responses of these neurons to an oriented edge are affected by changes in luminance contrast. However, in natural images, edges vary not only in contrast but also in the degree of blur, both because of changes in focus and also because shadows are not sharp. The effect of blur on the response dynamics of visual cortical neurons has not been explored. We presented luminance-defined single edges in the receptive fields of parafoveal (1–6 deg eccentric) V1 neurons of two macaque monkeys trained to fixate a spot of light. We varied the width of the blurred region of the edge stimuli up to 0.36 deg of visual angle. Even though the neurons responded robustly to stimuli that only contained high spatial frequencies and 0.36 deg is much larger than the limits of acuity at this eccentricity, changing the degree of blur had minimal effect on the responses of these neurons to the edge. Primates need to measure blur at the fovea to evaluate image quality and control accommodation, but this might only involve a specialist subpopulation of neurons. If visual cortical neurons in general responded differently to sharp and blurred stimuli, then this could provide a cue for form perception, for example, by helping to disambiguate the luminance edges created by real objects from those created by shadows. On the other hand, it might be important to avoid the distraction of changing blur as objects move in and out of the plane of fixation. Our results support the latter hypothesis: the responses of parafoveal V1 neurons are largely unaffected by changes in blur over a wide range.

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 Eye Movements Modulate Visual Receptive Fields of V4 Neurons

Neuron ◽  
2001 ◽  
Vol 29 (3) ◽  
pp. 757-767 ◽  
Author(s):  
Andreas S Tolias ◽  
Tirin Moore ◽  
Stelios M Smirnakis ◽  
Edward J Tehovnik ◽  
Athanassios G Siapas ◽  
...  
Keyword(s):  
Eye Movements ◽  
Receptive Fields ◽  
Visual Receptive Fields ◽  
V4 Neurons

scholarly journals Shape Interactions in Macaque Inferior Temporal Neurons

1999 ◽  
Vol 82 (1) ◽  
pp. 131-142 ◽  
Author(s):  
Marcus Missal ◽  
Rufin Vogels ◽  
Chao-Yi Li ◽  
Guy A. Orban
Keyword(s):  
Receptive Fields ◽  
Stimulus Position ◽  
Fixation Position ◽  
Shape Selective ◽  
Fixation Task ◽  
Object Parts

Missal et al. observed that the responses of inferior temporal (IT) neurons to a shape were reduced markedly when this shape partially overlapped a larger second shape, suggesting that shape interactions determine IT responses. In the present study, we compared the responses of IT neurons with combinations of two shapes which did or did not overlap and studied the effect of the relative and absolute positions of the two shapes. In a first test, a preferred shape (figure) was presented at the fixation point while a second, nonpreferred, shape was displayed either in the background of the figure (overlap) or at one of four peripheral positions (nonoverlap). Controls consisted of presentations of either shape in isolation at each of the five positions. The stimuli were presented during a fixation task. The responses to these combinations of two shapes were, on average, reduced compared with those elicited by the preferred shape presented in isolation. This suppression occurred whether or not the two shapes overlapped, but the degree of suppression in the overlap and nonoverlap conditions did not correlate. These interactions were stronger when the interacting stimulus was located in the contralateral compared with the ipsilateral hemifield. The position of the interacting stimulus within a hemifield significantly affected the suppression associated with combined shapes in some neurons. The strength of the interactions of the two nonoverlapping shapes depended on the shape of the interacting stimulus in half of the neurons. In a second test, the preferred shape and interacting stimulus could appear either at the fixation point or at one eccentric position. Here we found that the suppression was, on average, strongest when the interacting stimulus, rather than the preferred shape, was presented at the fixation position. Also, in 40% of the neurons, the response reduction was similar in overlap and nonoverlap conditions if effects of stimulus position were taken into account. In both tests, we also measured the responses to combinations of a nonpreferred shape and the interacting stimulus and showed that the response to a combination of two nonpreferred shapes was, in general, smaller than the response to a combination of the preferred and nonpreferred shape. Overall the results indicate that stimulus interactions in the receptive fields of IT neurons can be position and shape selective; this can contribute to the coding for the relationships between object parts.

Invariant Visual Responses From Attentional Gain Fields

1997 ◽  
Vol 77 (6) ◽  
pp. 3267-3272 ◽  
Author(s):  
Emilio Salinas ◽  
L. F. Abbott
Keyword(s):  
Spatial Scale ◽  
Computer Modeling ◽  
Visual Stimuli ◽  
Receptive Fields ◽  
Gain Modulation ◽  
Visual Responses ◽  
Translation Invariant ◽  
Modeling Methods ◽  
V4 Neurons ◽  
Substantial Degree

Salinas, Emilio and L. F. Abbott. Invariant visual responses from attentional gain fields. J. Neurophysiol. 77: 3267–3272, 1997. Inferotemporal (IT) neurons exhibit a substantial degree of invariance with respect to translation of images used as visual stimuli. Through theoretical and computer-modeling methods, we show how translation-invariant receptive fields, like those of IT neurons, can be generated from the responses of V4 neurons if the effects of attention are taken into account. The model incorporates a recently reported form of attention-dependent gain modulation in V4 and produces IT receptive fields that shift so they are centered at the point where attention is directed. Receptive fields of variable, attention-controlled spatial scale are obtained when the mechanism is extended to scale-dependent attentional gain fields. The results indicate that gain modulation may play analogous roles in the dorsal and ventral visual pathways, generating transformations from retinal coordinates to body- and object-centered systems, respectively.

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