Global Contour Saliency and Local Colinear Interactions

2002 ◽  
Vol 88 (5) ◽  
pp. 2846-2856 ◽  
Author(s):  
Wu Li ◽  
Charles D. Gilbert
Keyword(s):  
Limited Range ◽  
Average Density ◽  
Contour Integration ◽  
Contour Detection ◽  
Intermediate Step ◽  
Line Segments ◽  
Critical Range ◽  
Horizontal Connections ◽  
Line Elements ◽  
Contextual Interactions

Our visual system can link components of contours and segregate contours from complex backgrounds based on geometric grouping rules. This is an important intermediate step in object recognition. The substrate for contour integration may be based on contextual interactions and intrinsic horizontal connections seen in primary visual cortex (V1). We examined the perceptual rules governing contour saliency to determine whether the spatial extents of contextual interactions and horizontal connections match those mediating saliency. To quantify these rules, we used stimuli composed of randomly oriented nonoverlapping line segments. Salient contours within this complex background were formed by colinear alignment of nearby segments. Contour detectability was measured using a 2-interval-forced-choice design. Contour detectability deteriorated with increasing spacing between contour elements and improved as the number of colinear line elements was increased. At short contour spacing, the detectability reached a plateau with alignment of a few line segments that together formed a contour subtending several visual degrees. At intermediate spacing, saliency built up progressively with a greater number of colinear lines, extending up to 30°. When contour spacing was beyond a critical range (about 2°), however, the detectability dropped to chance levels, regardless of the number of colinear lines. Contour detectability was found to be a function not only of the relative spacing of contour elements with respect to the noise elements but also of the average density of the overall pattern. Furthermore, training significantly improved contour detection, increasing the critical spacing of line elements beyond which contours were no longer detectable. Our data suggest that global contour integration is based on mechanisms of limited spatial extent, comparable to the interactions observed in V1. These interactions can cascade over larger distances provided the spacing of stimulus elements is kept within a limited range.

scholarly journals How long range is contour integration in human color vision?

2003 ◽  
Vol 20 (1) ◽  
pp. 51-64 ◽  
Author(s):  
WILLIAM H.A. BEAUDOT ◽  
KATHY T. MULLEN
Keyword(s):  
Color Vision ◽  
Long Range ◽  
Short Range ◽  
Contour Integration ◽  
Contour Detection ◽  
Critical Element ◽  
Element Size ◽  
Human Color Vision ◽  
The Mean ◽  
Gabor Elements

We quantified and compared the effect of element spacing on contour integration between the achromatic (Ach), red–green (RG), and blue–yellow (BY) mechanisms. The task requires the linking of orientation across space to detect a contour in a stimulus composed of randomly oriented Gabor elements (1.5 cpd, σ = 0.17 deg), measured using a temporal 2AFC method. A contour of ten elements was pasted into a 10 × 10 cells array, and background elements were randomly positioned within the available cells. The effect of element spacing was investigated by varying the mean interelement distance between two and six times the period of the Gabor elements (λ = 0.66 deg) while the total number of elements was fixed. Contour detection was measured as a function of its curvature for jagged contours and for closed contours. At all curvatures, we found that performance for chromatic mechanisms declines more steeply with the increase in element separation than does performance for the achromatic mechanism. Averaged critical element separations were 4.6 ± 0.7, 3.6 ± 0.4, and 2.9 ± 0.2 deg for Ach, BY, and RG mechanisms, respectively. These results suggest that contour integration by the chromatic mechanisms relies more on short-range interactions in comparison to the achromatic mechanism. In a further experiment, we looked at the combined effect of element size and element separation in contour integration for the Ach mechanism.

scholarly journals Reduced influence of perceptual context in schizophrenia: behavioral and neurophysiological evidence

2019 ◽  
pp. 1-9 ◽  
Author(s):  
Victor J. Pokorny ◽  
Timothy J. Lano ◽  
Michael-Paul Schallmo ◽  
Cheryl A. Olman ◽  
Scott R. Sponheim
Keyword(s):  
Event Related Potentials ◽  
Contour Integration ◽  
Contour Detection ◽  
Group Differences ◽  
Neural Responses ◽  
Contour Perception ◽  
Accurate Perception ◽  
Visual Contour ◽  
Related Potentials ◽  
Intermediate Performance

Abstract Background Accurate perception of visual contours is essential for seeing and differentiating objects in the environment. Both the ability to detect visual contours and the influence of perceptual context created by surrounding stimuli are diminished in people with schizophrenia (SCZ). The central aim of the present study was to better understand the biological underpinnings of impaired contour integration and weakened effects of perceptual context. Additionally, we sought to determine whether visual perceptual abnormalities reflect genetic factors in SCZ and are present in other severe mental disorders. Methods We examined behavioral data and event-related potentials (ERPs) collected during the perception of simple linear contours embedded in similar background stimuli in 27 patients with SCZ, 23 patients with bipolar disorder (BP), 23 first-degree relatives of SCZ, and 37 controls. Results SCZ exhibited impaired visual contour detection while BP exhibited intermediate performance. The orientation of neighboring stimuli (i.e. flankers) relative to the contour modulated perception across all groups, but SCZ exhibited weakened suppression by the perceptual context created by flankers. Late visual (occipital P2) and cognitive (centroparietal P3) neural responses showed group differences and flanker orientation effects, unlike earlier ERPs (occipital P1 and N1). Moreover, behavioral effects of flanker context on contour perception were correlated with modulation in P2 & P3 amplitudes. Conclusion In addition to replicating and extending findings of abnormal contour integration and visual context modulation in SCZ, we provide novel evidence that the abnormal use of perceptual context is associated with higher-order sensory and cognitive processes.

scholarly journals Two-frequency analysis of interactions elicited by Vernier stimuli

2000 ◽  
Vol 17 (6) ◽  
pp. 959-973 ◽  
Author(s):  
JONATHAN D. VICTOR ◽  
MARY M. CONTE
Keyword(s):  
Frequency Analysis ◽  
Fourth Order ◽  
Receptive Fields ◽  
Orientation Tuning ◽  
Spatial Interactions ◽  
Line Segments ◽  
Sum Frequency ◽  
Horizontal Connections ◽  
Spatial Parameters ◽  
The Difference

In five subjects, we measured visual evoked potentials (VEPs) elicited by Vernier targets in which the contrast of the two components of the stimuli were modulated by sinusoids at distinct frequencies f1 and f2. This approach allows for the extraction of VEP signatures of spatial interactions, namely, responses at intermodulation frequencies n1f1 + n2f2, without the need to introduce motion into the stimulus. The most prominent interactions were at the sum frequency f1 + f2, and, for frequency pairs that were sufficiently separated, the difference frequency f1 − f2. These responses had a systematic dependence on the temporal parameters of the stimulus, corresponding to an effective latency of 145 to 165 ms. Fourth-order interactions were also detected, particularly at the frequencies 2f1 ± 2f2. These VEP signatures of interaction were similar to interactions seen for colinear line segments separated by a gap. Thus, for Vernier stimuli devoid of motion, VEP signatures of interaction are readily detected but are not specific to hyperacuity displacements. The distribution of interactions across harmonic orders is consistent with local rectification preceding the spatial interactions. Their effective latencies and dependence on spatial parameters are consistent with interactions within V1 receptive fields or mediated by horizontal connections between cells with a similar orientation tuning within V1.

scholarly journals Perceptual load modulates contour integration in conscious and unconscious states

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e7550 ◽  
Author(s):  
Kaiwen Cheng ◽  
Keyu Yang ◽  
Long Qin ◽  
Yixuan Zhuo ◽  
Hongmei Yan
Keyword(s):  
Perceptual Load ◽  
Contour Integration ◽  
Contour Detection ◽  
Cognitive Factors ◽  
Orientation Discrimination ◽  
Conscious Awareness ◽  
Sensory Features ◽  
High Level ◽  
Conscious Attention ◽  
Closure Effect

Previous research has documented that contour detection and integration may either be affected by local features such as the distances between elements or by high-level cognitive factors such as attention in our visual system. Less is known about how low and high level factors interact to influence contour integration. In this paper, we investigated how attention modulates contour integration through saliency (different element spacing) and topological propert ies (circle or S-shaped) when the state of conscious awareness is manipulated. A modified inattentional blindness (IB) combined with the Posner cuing paradigm was adopted in our three-phased experiment (unconscious-training-conscious). Attention was manipulated with high or low perceptual load for a foveal go/no-go task. Cuing effects were utilized to assess the covert processing of contours prior to a peripheral orientation discrimination task. We found that (1) salient circles and S-contours induced different cuing effects under low perceptual load but not with high load; (2) no consistent pattern of cuing effects was found for non-salient contours in all the conditions; (3) a positive cuing effect was observed for salient circles either consciously or unconsciously while a negative cuing effect occurred for salient S-contours only consciously. These results suggest that conscious awareness plays a pivotal role in coordinating a closure effect with the level of perceptual load. Only salient circles can be successfully integrated in an unconscious state under low perceptual load although both salient circles and S-contours can be done consciously. Our findings support a bi-directional mechanism that low-level sensory features interact with high-level cognitive factors in contour integration.

scholarly journals Axonal plasticity associated with perceptual learning in adult macaque primary visual cortex

2018 ◽  
Vol 115 (41) ◽  
pp. 10464-10469 ◽  
Author(s):  
Timo van Kerkoerle ◽  
Sally A. Marik ◽  
Stephan Meyer zum Alten Borgloh ◽  
Charles D. Gilbert
Keyword(s):  
Visual Cortex ◽  
Perceptual Learning ◽  
Primary Visual Cortex ◽  
Detection Task ◽  
Contour Detection ◽  
Cortical Lesion ◽  
Axon Collaterals ◽  
Horizontal Connections ◽  
Cortical Regions ◽  
Axonal Arbors

Perceptual learning is associated with changes in the functional properties of neurons even in primary sensory areas. In macaque monkeys trained to perform a contour detection task, we have observed changes in contour-related facilitation of neuronal responses in primary visual cortex that track their improvement in performance on a contour detection task. We have previously explored the anatomical substrate of experience-dependent changes in the visual cortex based on a retinal lesion model, where we find sprouting and pruning of the axon collaterals in the cortical lesion projection zone. Here, we attempted to determine whether similar changes occur under normal visual experience, such as that associated with perceptual learning. We labeled the long-range horizontal connections in visual cortex by virally mediated transfer of genes expressing fluorescent probes, which enabled us to do longitudinal two-photon imaging of axonal arbors over the period during which animals improve in contour detection performance. We found that there are substantial changes in the axonal arbors of neurons in cortical regions representing the trained part of the visual field, with sprouting of new axon collaterals and pruning of preexisting axon collaterals. Our findings indicate that changes in the structure of axonal arbors are part of the circuit-level mechanism of perceptual learning, and further support the idea that the learned information is encoded at least in part in primary visual cortex.

scholarly journals The effect of low temperature on hens' eggs

1925 ◽  
Vol 98 (691) ◽  
pp. 436-456 ◽  
Keyword(s):  
Low Temperature ◽  
Silicic Acid ◽  
Critical Length ◽  
Limited Range ◽  
Peculiar Feature ◽  
Freezing And Thawing ◽  
Original State ◽  
Critical Range ◽  
Time Changes

Colloids when frozen do not as a rule recover their original state on thawing. Stiles quotes many such cases, a well-known example being a gel of silicic acid which is separated by freezing and thawing into a mixture of water and solid flakes of acid. Similarly, when a solution of chlorophyll in water is frozen slowly, the chlorophyll on thawing is found to be aggregated into large flocks which slowly settle to the bottom. Recovery of state, however, takes place in certain systems, not necessarily the simplest, if the rate of freezing be high enough. The solution of chlorophyll furnishes an example. If it be frozen in liquid air it completely recovers its original state on thawing. Obviously the end temperature does not matter because it may be said with certainty that the frozen mass could be kept at the temperature of liquid air indefinitely without losing the capacity of reforming a solution on thawing. There must therefore exist a certain limited range of temperature within which alone the process of desolution can occur. Let us call this the critical range. The peculiar feature of any temperature within the critical range θ 1 - θ 2 is that, if the system be kept at that temperature for a critical length T of time, changes take place which are not reversed on thawing.

scholarly journals Reduced Influence of Perceptual Context in Schizophrenia: Behavioral and Neurophysiological Evidence

2019 ◽  
Author(s):  
Victor J. Pokorny ◽  
Timothy J. Lano ◽  
Michael-Paul Schallmo ◽  
Cheryl A. Olman ◽  
Scott R. Sponheim
Keyword(s):  
Bipolar Disorder ◽  
Event Related Potentials ◽  
Contour Integration ◽  
Contour Detection ◽  
Group Differences ◽  
Neural Responses ◽  
Contour Perception ◽  
Accurate Perception ◽  
Visual Contour ◽  
Related Potentials

AbstractBackgroundAccurate perception of visual contours is essential for seeing and differentiating objects in the environment. Both the ability to detect visual contours and the influence of perceptual context created by surrounding stimuli are diminished in people with schizophrenia. The central aim of the present study was to better understand the biological underpinnings of impaired contour integration and weakened effects of perceptual context. Additionally, we sought to determine whether visual perceptual abnormalities reflect genetic factors in schizophrenia and are present in other severe mental disorders.MethodsWe examined behavioral data and event-related potentials (ERPs) collected during the perception of simple linear contours embedded in similar background stimuli in 27 patients with schizophrenia (SCZ), 23 patients with bipolar disorder, 23 first-degree relatives of SCZ and 37 controls.ResultsSCZ exhibited impaired visual contour detection while patients with bipolar disorder exhibited intermediate performance. The orientation of neighboring stimuli (i.e., flankers) relative to the contour modulated perception across all groups, but SCZ exhibited weakened suppression by the perceptual context created by flankers. Late visual (occipital P2) and cognitive (centroparietal P3) neural responses showed group differences and flanker orientation effects, unlike earlier ERPs (occipital P1 and N1). Moreover, behavioral effects of flanker context on contour perception were correlated with modulation in P2/P3 amplitudes.ConclusionIn addition to replicating and extending findings of abnormal contour integration and visual context modulation in SCZ, we provide novel evidence that abnormal use of perceptual context is associated with higher-order sensory and cognitive processes.

THE HEAT CAPACITY AT CONSTANT VOLUME OF THE SYSTEM ETHYLENE NEAR THE CRITICAL TEMPERATURE AND PRESSURE

1938 ◽  
Vol 16b (7) ◽  
pp. 230-241 ◽  
Author(s):  
D. B. Pall ◽  
J. W. Broughton ◽  
O. Maass
Keyword(s):  
Heat Capacity ◽  
Critical Temperature ◽  
Thermal Treatment ◽  
Molecular Interaction ◽  
Liquid State ◽  
Average Density ◽  
Constant Volume ◽  
Critical Range ◽  
Temperature And Pressure

The heat capacity of ethylene at constant volume has been investigated through the critical range, between 6.5° and 27 °C., at an average density slightly greater than the critical. The heat capacity in the immediate neighborhood of the critical temperature is found to be a function of the previous thermal treatment of the system. The results indicate the persistence of a large amount of molecular interaction in ethylene above the critical temperature, and are in agreement with the concept that the liquid state of aggregation can persist above the temperature at which the visible meniscus disappears.

scholarly journals The role of sensory uncertainty in simple contour integration

2020 ◽  
Vol 16 (11) ◽  
pp. e1006308
Author(s):  
Yanli Zhou ◽  
Luigi Acerbi ◽  
Wei Ji Ma
Keyword(s):  
Bayesian Inference ◽  
Perceptual Organization ◽  
Contour Integration ◽  
Retinal Eccentricity ◽  
Bayesian Decision ◽  
Line Segments ◽  
Separate Line ◽  
Sensory Uncertainty ◽  
Sensory Noise

Perceptual organization is the process of grouping scene elements into whole entities. A classic example is contour integration, in which separate line segments are perceived as continuous contours. Uncertainty in such grouping arises from scene ambiguity and sensory noise. Some classic Gestalt principles of contour integration, and more broadly, of perceptual organization, have been re-framed in terms of Bayesian inference, whereby the observer computes the probability that the whole entity is present. Previous studies that proposed a Bayesian interpretation of perceptual organization, however, have ignored sensory uncertainty, despite the fact that accounting for the current level of perceptual uncertainty is one of the main signatures of Bayesian decision making. Crucially, trial-by-trial manipulation of sensory uncertainty is a key test to whether humans perform near-optimal Bayesian inference in contour integration, as opposed to using some manifestly non-Bayesian heuristic. We distinguish between these hypotheses in a simplified form of contour integration, namely judging whether two line segments separated by an occluder are collinear. We manipulate sensory uncertainty by varying retinal eccentricity. A Bayes-optimal observer would take the level of sensory uncertainty into account—in a very specific way—in deciding whether a measured offset between the line segments is due to non-collinearity or to sensory noise. We find that people deviate slightly but systematically from Bayesian optimality, while still performing “probabilistic computation” in the sense that they take into account sensory uncertainty via a heuristic rule. Our work contributes to an understanding of the role of sensory uncertainty in higher-order perception.

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