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Uncovering foveal crowding?

Lev M, Yehezkel O, Polat U - Sci Rep (2014)

Bottom Line: We hypothesized that limiting stimulus availability should decrease object recognition in clutter.Here we show, for the first time, that robust contour interactions exist in the fovea for much larger target-flanker spacing than reported previously: participants overcome crowded conditions for long presentations times but exhibit contour interaction effects for short presentation times.Our results suggest that contemporary models of context modulation should include both time and spatial processing.

View Article: PubMed Central - PubMed

Affiliation: Goldschleger Eye Research Institute, the Sackler Faculty of Medicine, Tel-Aviv University, Tel-Hashomer, Israel.

ABSTRACT
Visual crowding, as context modulation, reduce the ability to recognize objects in clutter, sets a fundamental limit on visual perception and object recognition. It's considered that crowding does not exist in the fovea and extensive efforts explored crowding in the periphery revealed various models that consider several aspects of spatial processing. Studies showed that spatial and temporal crowding are correlated, suggesting a tradeoff between spatial and temporal processing of crowding. We hypothesized that limiting stimulus availability should decrease object recognition in clutter. Here we show, for the first time, that robust contour interactions exist in the fovea for much larger target-flanker spacing than reported previously: participants overcome crowded conditions for long presentations times but exhibit contour interaction effects for short presentation times. Thus, by enabling enough processing time in the fovea, contour interactions can be overcome, enabling object recognition. Our results suggest that contemporary models of context modulation should include both time and spatial processing.

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Related in: MedlinePlus

Backward masking reveals a crowding effect at the fovea. a) Stimuli-target and crowded conditions were the same as in Figure 1.After the presentation time, a mask consisting of random Es, separated by one letter spacing, appeared after inter stimulus intervals from 30 to 120 msec. The task of the subject was to report the opening direction of the target E under the single and crowded conditions. The dashed lines indicate the response level for no backward masking conditions (baseline inter stimulus interval = 0). b, d) The percentage correct (y axis) for the single (uncrowded, red line) and crowded (blue line) conditions are plotted against the inter stimulus interval (x axis) for presentation times of 60 (b) and 30 (d) msec. c,e) The reaction time in msec (reaction time, y axis) is plotted against inter stimulus interval (x axis) for presentation times of 60 (c) and 30 (e) msec. There was a significant effect of contour interaction for both stimulus durations in both the percent correct and the reaction time.
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f4: Backward masking reveals a crowding effect at the fovea. a) Stimuli-target and crowded conditions were the same as in Figure 1.After the presentation time, a mask consisting of random Es, separated by one letter spacing, appeared after inter stimulus intervals from 30 to 120 msec. The task of the subject was to report the opening direction of the target E under the single and crowded conditions. The dashed lines indicate the response level for no backward masking conditions (baseline inter stimulus interval = 0). b, d) The percentage correct (y axis) for the single (uncrowded, red line) and crowded (blue line) conditions are plotted against the inter stimulus interval (x axis) for presentation times of 60 (b) and 30 (d) msec. c,e) The reaction time in msec (reaction time, y axis) is plotted against inter stimulus interval (x axis) for presentation times of 60 (c) and 30 (e) msec. There was a significant effect of contour interaction for both stimulus durations in both the percent correct and the reaction time.

Mentions: This dependency of the effect of contour interaction on presentation time in the fovea of young and presbyopic participants is novel and is not predicted by the contemporary models of crowding128 that explicitly assume that there is no crowding effect in the fovea (and they may regard this effect as different than crowding). Thus, we hypothesized that limiting the stimulus availability will reveal the spatial crowding effect even in cases where the spacing is larger, as shown in Fig. 1. Therefore, we imposed the condition of backward masking (Figure 4a), which interferes with the processing of the target232425 and enables one to estimate the processing time. We found, consistent with our hypothesis, that contour interaction appears when the stimulus availability is limited (Figure 4b). The results show the robust effect of a reduced percent of correct responses for presentation times of 30 and 60 msec in which the percent correct is reduced remarkably and significantly (paired t-test, p = 0.0002 time duration = 30; p = 0.0005 time duration = 60) between 30 and 120 msec of inter-stimulus intervals. Interestingly, the effect of backward masking on the crowded conditions is much stronger, reducing the percent correct from 92% to 66% for short inter-stimulus intervals. However, for the target alone, the effect of backward masking is lower and maximal for a time duration of 30 msec, where the percent correct was reduced from 96% to 77% for a shorter inter-stimulus interval of 30 msec. The effect of backward masking on the target alone (return to the dashed lines) diminished after stimulus asynchrony onset of 120 msec (presentation time + inter-stimulus interval), whereas under the crowded conditions the effect is apparent for after stimulus asynchrony onset of more than 180 msec. Thus, for the target alone, a stimulus availability of 120 msec is enough for correct processing, whereas under the crowded conditions the stimulus availability needs to be much longer to correct the processing of the target. This result supports the idea that crowded conditions impose longer processing times. In parallel to the backward masking effect on the percent correct, the reaction time becomes significantly slower (paired t-test, p = 0.00001 time duration = 30; p = 0.0001 time duration = 60) in all cases of backward masking, ranging from 50–140 mesc under the crowded conditions. These results clearly show that processing of letter recognition under crowded conditions requires more processing effort, as revealed by the longer time needed for decision (reaction time).


Uncovering foveal crowding?

Lev M, Yehezkel O, Polat U - Sci Rep (2014)

Backward masking reveals a crowding effect at the fovea. a) Stimuli-target and crowded conditions were the same as in Figure 1.After the presentation time, a mask consisting of random Es, separated by one letter spacing, appeared after inter stimulus intervals from 30 to 120 msec. The task of the subject was to report the opening direction of the target E under the single and crowded conditions. The dashed lines indicate the response level for no backward masking conditions (baseline inter stimulus interval = 0). b, d) The percentage correct (y axis) for the single (uncrowded, red line) and crowded (blue line) conditions are plotted against the inter stimulus interval (x axis) for presentation times of 60 (b) and 30 (d) msec. c,e) The reaction time in msec (reaction time, y axis) is plotted against inter stimulus interval (x axis) for presentation times of 60 (c) and 30 (e) msec. There was a significant effect of contour interaction for both stimulus durations in both the percent correct and the reaction time.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3921636&req=5

f4: Backward masking reveals a crowding effect at the fovea. a) Stimuli-target and crowded conditions were the same as in Figure 1.After the presentation time, a mask consisting of random Es, separated by one letter spacing, appeared after inter stimulus intervals from 30 to 120 msec. The task of the subject was to report the opening direction of the target E under the single and crowded conditions. The dashed lines indicate the response level for no backward masking conditions (baseline inter stimulus interval = 0). b, d) The percentage correct (y axis) for the single (uncrowded, red line) and crowded (blue line) conditions are plotted against the inter stimulus interval (x axis) for presentation times of 60 (b) and 30 (d) msec. c,e) The reaction time in msec (reaction time, y axis) is plotted against inter stimulus interval (x axis) for presentation times of 60 (c) and 30 (e) msec. There was a significant effect of contour interaction for both stimulus durations in both the percent correct and the reaction time.
Mentions: This dependency of the effect of contour interaction on presentation time in the fovea of young and presbyopic participants is novel and is not predicted by the contemporary models of crowding128 that explicitly assume that there is no crowding effect in the fovea (and they may regard this effect as different than crowding). Thus, we hypothesized that limiting the stimulus availability will reveal the spatial crowding effect even in cases where the spacing is larger, as shown in Fig. 1. Therefore, we imposed the condition of backward masking (Figure 4a), which interferes with the processing of the target232425 and enables one to estimate the processing time. We found, consistent with our hypothesis, that contour interaction appears when the stimulus availability is limited (Figure 4b). The results show the robust effect of a reduced percent of correct responses for presentation times of 30 and 60 msec in which the percent correct is reduced remarkably and significantly (paired t-test, p = 0.0002 time duration = 30; p = 0.0005 time duration = 60) between 30 and 120 msec of inter-stimulus intervals. Interestingly, the effect of backward masking on the crowded conditions is much stronger, reducing the percent correct from 92% to 66% for short inter-stimulus intervals. However, for the target alone, the effect of backward masking is lower and maximal for a time duration of 30 msec, where the percent correct was reduced from 96% to 77% for a shorter inter-stimulus interval of 30 msec. The effect of backward masking on the target alone (return to the dashed lines) diminished after stimulus asynchrony onset of 120 msec (presentation time + inter-stimulus interval), whereas under the crowded conditions the effect is apparent for after stimulus asynchrony onset of more than 180 msec. Thus, for the target alone, a stimulus availability of 120 msec is enough for correct processing, whereas under the crowded conditions the stimulus availability needs to be much longer to correct the processing of the target. This result supports the idea that crowded conditions impose longer processing times. In parallel to the backward masking effect on the percent correct, the reaction time becomes significantly slower (paired t-test, p = 0.00001 time duration = 30; p = 0.0001 time duration = 60) in all cases of backward masking, ranging from 50–140 mesc under the crowded conditions. These results clearly show that processing of letter recognition under crowded conditions requires more processing effort, as revealed by the longer time needed for decision (reaction time).

Bottom Line: We hypothesized that limiting stimulus availability should decrease object recognition in clutter.Here we show, for the first time, that robust contour interactions exist in the fovea for much larger target-flanker spacing than reported previously: participants overcome crowded conditions for long presentations times but exhibit contour interaction effects for short presentation times.Our results suggest that contemporary models of context modulation should include both time and spatial processing.

View Article: PubMed Central - PubMed

Affiliation: Goldschleger Eye Research Institute, the Sackler Faculty of Medicine, Tel-Aviv University, Tel-Hashomer, Israel.

ABSTRACT
Visual crowding, as context modulation, reduce the ability to recognize objects in clutter, sets a fundamental limit on visual perception and object recognition. It's considered that crowding does not exist in the fovea and extensive efforts explored crowding in the periphery revealed various models that consider several aspects of spatial processing. Studies showed that spatial and temporal crowding are correlated, suggesting a tradeoff between spatial and temporal processing of crowding. We hypothesized that limiting stimulus availability should decrease object recognition in clutter. Here we show, for the first time, that robust contour interactions exist in the fovea for much larger target-flanker spacing than reported previously: participants overcome crowded conditions for long presentations times but exhibit contour interaction effects for short presentation times. Thus, by enabling enough processing time in the fovea, contour interactions can be overcome, enabling object recognition. Our results suggest that contemporary models of context modulation should include both time and spatial processing.

Show MeSH
Related in: MedlinePlus