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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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Contour interaction effect at the fovea – one letter spacing: Data is presented for 11 participants.a) The target was letter E (single) and the subject's task was to report the open direction of the E. In crowded cases, the target E was embedded in an array of other randomly oriented Es, separated by spacing of one letter. The task of the subject was to report the opening direction of the letter E under both conditions. b) The percentage correct (y axis) for the single (uncrowded, red line) and crowded (blue line) conditions are plotted against the stimulus duration (x axis). The letter size was 0.18 deg. and the target-spacing was one letter size c) The reaction time in msec (y axis) is plotted against the stimulus duration (x axis). There was no significant effect of contour interaction for all stimulus durations. The reaction time for the crowded conditions was always significantly slower by about 50 msec.
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f1: Contour interaction effect at the fovea – one letter spacing: Data is presented for 11 participants.a) The target was letter E (single) and the subject's task was to report the open direction of the E. In crowded cases, the target E was embedded in an array of other randomly oriented Es, separated by spacing of one letter. The task of the subject was to report the opening direction of the letter E under both conditions. b) The percentage correct (y axis) for the single (uncrowded, red line) and crowded (blue line) conditions are plotted against the stimulus duration (x axis). The letter size was 0.18 deg. and the target-spacing was one letter size c) The reaction time in msec (y axis) is plotted against the stimulus duration (x axis). There was no significant effect of contour interaction for all stimulus durations. The reaction time for the crowded conditions was always significantly slower by about 50 msec.

Mentions: First, we measured the contour interaction effect as a function of temporal durations of the target presentation. We used a method originally termed “contour interactions” to measure the surround effect on recognition of a single E letter321. Here, we manipulated the presentation time of the stimuli. The E target was presented for presentation times between 30 to 120 msec, either alone or embedded between a surround array of E letters3 (Fig. 1a). First, the spacing between the target and the surround was one letter size (0.18 deg., 10.8 arc min, VA = 0.3 LogMar) larger than the critical distance known to produce crowding1248. The observer's task was to report whether the E was pointing to the right or to the left side. The results show (Fig. 1b), as expected, that there is no effect for all durations. There was a slight reduction in the percentage of correct answers at a presentation time of 30 and 60 msec from 96% to 92% and from 98% to 95%, respectively, but the effect is not significant (paired t-test, p = 0.2618). However, when inspecting the reaction time, the results clearly show (Fig. 1c) that there is a consistent and significant (paired t-test, p = 0.0007) reduction of about 50 msec under the crowding conditions for all presentation times. These results suggest that extra processing time is required to overcome the effect of contour interaction in the fovea.


Uncovering foveal crowding?

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

Contour interaction effect at the fovea – one letter spacing: Data is presented for 11 participants.a) The target was letter E (single) and the subject's task was to report the open direction of the E. In crowded cases, the target E was embedded in an array of other randomly oriented Es, separated by spacing of one letter. The task of the subject was to report the opening direction of the letter E under both conditions. b) The percentage correct (y axis) for the single (uncrowded, red line) and crowded (blue line) conditions are plotted against the stimulus duration (x axis). The letter size was 0.18 deg. and the target-spacing was one letter size c) The reaction time in msec (y axis) is plotted against the stimulus duration (x axis). There was no significant effect of contour interaction for all stimulus durations. The reaction time for the crowded conditions was always significantly slower by about 50 msec.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Contour interaction effect at the fovea – one letter spacing: Data is presented for 11 participants.a) The target was letter E (single) and the subject's task was to report the open direction of the E. In crowded cases, the target E was embedded in an array of other randomly oriented Es, separated by spacing of one letter. The task of the subject was to report the opening direction of the letter E under both conditions. b) The percentage correct (y axis) for the single (uncrowded, red line) and crowded (blue line) conditions are plotted against the stimulus duration (x axis). The letter size was 0.18 deg. and the target-spacing was one letter size c) The reaction time in msec (y axis) is plotted against the stimulus duration (x axis). There was no significant effect of contour interaction for all stimulus durations. The reaction time for the crowded conditions was always significantly slower by about 50 msec.
Mentions: First, we measured the contour interaction effect as a function of temporal durations of the target presentation. We used a method originally termed “contour interactions” to measure the surround effect on recognition of a single E letter321. Here, we manipulated the presentation time of the stimuli. The E target was presented for presentation times between 30 to 120 msec, either alone or embedded between a surround array of E letters3 (Fig. 1a). First, the spacing between the target and the surround was one letter size (0.18 deg., 10.8 arc min, VA = 0.3 LogMar) larger than the critical distance known to produce crowding1248. The observer's task was to report whether the E was pointing to the right or to the left side. The results show (Fig. 1b), as expected, that there is no effect for all durations. There was a slight reduction in the percentage of correct answers at a presentation time of 30 and 60 msec from 96% to 92% and from 98% to 95%, respectively, but the effect is not significant (paired t-test, p = 0.2618). However, when inspecting the reaction time, the results clearly show (Fig. 1c) that there is a consistent and significant (paired t-test, p = 0.0007) reduction of about 50 msec under the crowding conditions for all presentation times. These results suggest that extra processing time is required to overcome the effect of contour interaction in the fovea.

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