scholarly journals Nonsymbolic numerosity in sets with illusory-contours exploits a context-sensitive, but contrast-insensitive, visual boundary formation process

2021 ◽  
Author(s):  
Andrea Adriano ◽  
Luca Rinaldi ◽  
Luisa Girelli
Keyword(s):  
Numerical Representation ◽  
Illusory Contours ◽  
Boundary Formation ◽  
Contrast Polarity ◽  
Context Sensitive ◽  
Visual Boundary ◽  
Brightness Enhancement ◽  
Texture Density ◽  
Numerical Discrimination ◽  
Opposite Contrast

AbstractThe visual mechanisms underlying approximate numerical representation are still intensely debated because numerosity information is often confounded with continuous sensory cues (e.g., texture density, area, convex hull). However, numerosity is underestimated when a few items are connected by illusory contours (ICs) lines without changing other physical cues, suggesting in turn that numerosity processing may rely on discrete visual input. Yet, in these previous works, ICs were generated by black-on-gray inducers producing an illusory brightness enhancement, which could represent a further continuous sensory confound. To rule out this possibility, we tested participants in a numerical discrimination task in which we manipulated the alignment of 0, 2, or 4 pairs of open/closed inducers and their contrast polarity. In Experiment 1, aligned open inducers had only one polarity (all black or all white) generating ICs lines brighter or darker than the gray background. In Experiment 2, open inducers had always opposite contrast polarity (one black and one white inducer) generating ICs without strong brightness enhancement. In Experiment 3, reverse-contrast inducers were aligned but closed with a line preventing ICs completion. Results showed that underestimation triggered by ICs lines was independent of inducer contrast polarity in both Experiment 1 and Experiment 2, whereas no underestimation was found in Experiment 3. Taken together, these results suggest that mere brightness enhancement is not the primary cause of the numerosity underestimation induced by ICs lines. Rather, a boundary formation mechanism insensitive to contrast polarity may drive the effect, providing further support to the idea that numerosity processing exploits discrete inputs.

scholarly journals Masking by edge-induced illusory contours depends on contrast polarity

2010 ◽  
Vol 3 (9) ◽  
pp. 654-654
Author(s):  
L. Barghout ◽  
S. E Palmer ◽  
C. W Tyler
Keyword(s):  
Illusory Contours ◽  
Contrast Polarity

scholarly journals Binocular Capture: The effects of mismatched Spatial frequency and opposite contrast polarity

2010 ◽  
Vol 10 (7) ◽  
pp. 368-368
Author(s):  
A. Raghunandan ◽  
S. Andrus ◽  
L. Nennig
Keyword(s):  
Spatial Frequency ◽  
Contrast Polarity ◽  
Opposite Contrast

Contrast Polarity Affects Performance after Figure-Ground Coding

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 243-243
Author(s):  
K J Linnell ◽  
G W Humphreys
Keyword(s):  
Experimental Psychology ◽  
Reaction Times ◽  
Human Perception ◽  
Opposite Polarity ◽  
Regular Polygons ◽  
Target Element ◽  
Dramatic Effect ◽  
Contrast Polarity ◽  
Search Experiment ◽  
Opposite Contrast

Gilchrist et al (1997 Journal of Experimental Psychology: Human Perception and Performance23 464 – 480) proposed that some aspects of grouping are relatively insensitive to variations in contrast polarity between the elements to be grouped. We assessed the contrast-polarity sensitivity of grouping in a visual search experiment. Display elements were corner-brackets arranged at the vertices of regular polygons (see Donnelly et al, 1991 Journal of Experimental Psychology: Human Perception and Performance17 561 – 570), either aligned with polygon sides (strong-grouping condition), rotated through 20° (weak-grouping condition), or rotated through 180° (open condition). The background was grey; on same-contrast-polarity trials, elements were either all white or all black; on opposite-polarity trials, each element was white and black. The task was to detect a target element rotated 180° with respect to the others. With weak grouping present, opposite contrast polarity slowed reaction times dramatically: they were as slow as those to open displays. A second experiment in which display elements were pacmen showed that the contrast-polarity effect on performance is modulated by figure - ground relations: the dramatic effect of contrast polarity in the weak-grouping condition disappeared, presumably because search focused on the uniform grey illusory surface. These results suggest that grouping operates automatically to produce figure - ground coding of displays, but that contrast polarity differences within a figural surface affect the output of these codes to systems concerned with perceptual discriminations.

Brightness perception, illusory contours, and corticogeniculate feedback

1995 ◽  
Vol 12 (6) ◽  
pp. 1027-1052 ◽  
Author(s):  
Alan Gove ◽  
Stephen Grossberg ◽  
Ennio Mingolla
Keyword(s):  
Feedback Loop ◽  
Receptive Fields ◽  
Brightness Distribution ◽  
Illusory Contours ◽  
Cortical Cells ◽  
Context Sensitive ◽  
Matching Process ◽  
Generate Surface ◽  
Boundary Representations ◽  
Surface Representations

AbstractA neural network model is developed to explain how visual thalamocortical interactions give rise to boundary percepts such as illusory contours and surface percepts such as filled-in brightnesses. Top-down feedback interactions are needed in addition to bottom-up feed-forward interactions to simulate these data. One feedback loop is modeled between lateral geniculate nucleus (LGN) and cortical area V1, and another within cortical areas V1 and V2. The first feedback loop realizes a matching process which enhances LGN cell activities that are consistent with those of active cortical cells, and suppresses LGN activities that are not. This corticogeniculate feedback, being endstopped and oriented, also enhances LGN ON cell activations at the ends of thin dark lines, thereby leading to enhanced cortical brightness percepts when the lines group into closed illusory contours. The second feedback loop generates boundary representations, including illusory contours, that coherently bind distributed cortical features together. Brightness percepts form within the surface representations through a diffusive filling-in process that is contained by resistive gating signals from the boundary representations. The model is used to simulate illusory contours and surface brightnesses induced by Ehrenstein disks, Kanizsa squares, Glass patterns, and cafe wall patterns in single contrast, reverse contrast, and mixed contrast configurations. These examples illustrate how boundary and surface mechanisms can generate percepts that are highly context-sensitive, including how illusory contours can be amodally recognized without being seen, how model simple cells in V1 respond preferentially to luminance discontinuities using inputs from both LGN ON and OFF cells, how model bipole cells in V2 with two colinear receptive fields can help to complete curved illusory contours, how short-range simple cell groupings and long-range bipole cell groupings can sometimes generate different outcomes, and how model double-opponent, filling-in and boundary segmentation mechanisms in V4 interact to generate surface brightness percepts in which filling-in of enhanced brightness and darkness can occur before the net brightness distribution is computed by double-opponent interactions.

Contrast Configuration Influences Grouping in Apparent Motion

Perception ◽  
10.1068/p3444 ◽  
2005 ◽  
Vol 34 (6) ◽  
pp. 669-685 ◽  
Author(s):  
Anna Ma-Wyatt ◽  
Colin W G Clifford ◽  
Peter Wenderoth
Keyword(s):  
Apparent Motion ◽  
Contrast Polarity ◽  
Ternus Display ◽  
Static Display ◽  
Stereo Display ◽  
Motion Responses ◽  
Group Motion ◽  
Similar Dependence ◽  
Opposite Contrast

We investigated whether the same principles that influence grouping in static displays also influence grouping in apparent motion. Using the Ternus display, we found that the proportion of group motion reports was influenced by changes in contrast configuration. Subjects made judgments of completion of these same configurations in a static display. Generally, contrast configurations that induced a high proportion of group motion responses were judged as more ‘complete’ in static displays. Using a stereo display, we then tested whether stereo information and T-junction information were critical for this increase in group motion. Perceived grouping was consistently higher for same contrast polarity configurations than for opposite contrast polarity configurations, regardless of the presence of stereo information or explicit T-junctions. Thus, while grouping in static and moving displays showed a similar dependence on contrast configuration, motion grouping showed little dependence on stereo or T-junction information.

scholarly journals A comparison of tests for quantifying sensory eye dominance

2017 ◽  
Author(s):  
Manuela Bossi ◽  
Lisa Hamm ◽  
Annegret Dahlmann-Noor ◽  
Steven C. Dakin
Keyword(s):  
Test Validity ◽  
Good Test ◽  
Retest Reliability ◽  
Contrast Polarity ◽  
Eye Dominance ◽  
Comparison Of Tests ◽  
Opposite Contrast ◽  
Test Retest Reliability ◽  
Sensory Eye Dominance ◽  
Sensory Dominance

AbstractClinicians rely heavily on stereoacuity to measure binocular visual function, but stereo-vision represents only one aspect of binocularity. Lab-based tests of sensory eye dominance (SED) are commonplace, but have not been translated to wider clinical practice. Here we compare several methods of quantifying SED in a format suitable for clinical use. We tested 30 participants with ostensibly normal vision on 8 tests. Seven tests (#1-7) were designed to quantify SED in the form of an interocular balance-point (BP). In tests #1-6, we estimated a contrast-BP, the interocular difference in contrast required for observers to be equally likely to base their judgement on either eye, whereas in test #7 we measured binocular rivalry (interocular ratio of sensory dominance duration). We compare test-retest reliability (intra-observer consistency) and test-validity (inter-observer discriminatory power) and compare BP to stereoacuity (test #8). The test that best preserved inter-observer differences in contrast balance while maintaining good test-retest reliability was a polarity judgement using superimposed opposite-contrast polarity same-identity optotypes. A reliable and valid measure of SED can be obtained rapidly (20 trials) using a simple contrast-polarity judgement. Tests that use polarity-rivalrous stimuli elicit more reliable judgments than those that do not.Significance StatementAlthough sensory eye dominance is central to understanding normal and disordered binocular vision, there is currently no consensus as to the best way to measure it. Here we compare several candidate measures of sensory eye dominance and conclude that a reliable measure of SED can be achieved rapidly using a judgement of stimulus contrast-polarity.

Contrast and Contextual Effects: Detection of Subthreshold Lines

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 177-177 ◽  
Author(s):  
C Wehrhahn ◽  
B Dresp
Keyword(s):  
Visual Processing ◽  
Contextual Effects ◽  
Detection Thresholds ◽  
Preliminary Results ◽  
Contrast Polarity ◽  
Early Stages ◽  
Relative Contrast ◽  
Mere Presence ◽  
Opposite Contrast

Contextual effects of collinear lines and features on the processing of line targets, finding expression in detection facilitation, have been described recently in the literature (Dresp and Bonnet, 1995 Vision Research35 1071 – 1078; Kapadia, Ito, Gilbert, and Westheimer, 1995 Neuron15 843 – 856). We are reporting a study of the effects of contrast intensity and contrast polarity on these contextual effects. Thin subthreshold lines, not detectable on a plain background, were flashed at a position collinear with a context line of varying luminance and polarity. A temporal 2AFC procedure was used to determine detection thresholds. The mere presence of a collinear context line of weak contrast, regardless of its polarity, was found to make the subthreshold lines detectable. For target lines and context lines of the same contrast polarity, increasing context contrast first enhances, then diminishes, target detectability. For target lines and context lines of opposite contrast polarity, increasing context contrast enhances target detectability. These preliminary results indicate that contrast intensity and relative contrast polarity interact in the genesis of grouping effects or contextual effects at early stages of visual processing.

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