Collinear facilitation is a common phenomenon in the fovea, but it has been recently challenged at the human periphery. Since physiological studies show that facilitation is found at the periphery but only from outside the receptive field, our hypothesis was that facilitation at the periphery exists but from larger target-flanker separations than the fovea. Here, we applied a recent paradigm (Polat & Sagi, 2007) to probe facilitation at the periphery. We used a Yes/No detection task by measuring the false-positive reports (false-alarm, pfa) and hit-rate (phit) for a low-contrast Gabor target (between two flankers) that appeared randomly at the fovea or at the periphery (2° or 4°) to the right or left side. We used different target-flanker separations and orientations at the fovea and at the periphery. Importantly, we found that phit is affected by the target-flanker separations and orientations. Short distances show a suppression effect, but the range of suppression increases with increasing eccentricity. A facilitation effect was found for collinear configuration outside of the suppression range. A similar effect was found for the decisional criterion (Cr), which was correlated with suppression (positive) and facilitation (negative). All together, our results indicate that facilitation exists at the periphery when the target-flanker distance is properly scaled. Thus, our results indicate that collinear facilitation is a common phenomenon that exists in both the periphery and fovea. The suppression range indicates that the perceptual receptive field increases with increasing eccentricity. Our results provide a working hypothesis that explains the functional differences found between the fovea and the periphery. This supports the basic phenomena underlying visual perception, such as collinear facilitation, visual crowding, and backward masking.

Presbyopia, from the Greek for aging eye, is, like death and taxes, inevitable. Presbyopia causes near vision to degrade with age, affecting virtually everyone over the age of 50. Presbyopia has multiple negative effects on the quality of vision and the quality of life, due to limitations on daily activities – in particular, reading. In addition presbyopia results in reduced near visual acuity, reduced contrast sensitivity, and slower processing speed. Currently available solutions, such as optical corrections, are not ideal for all daily activities. Here we show that perceptual learning (repeated practice on a demanding visual task) results in improved visual performance in presbyopes, enabling them to overcome and/or delay some of the disabilities imposed by the aging eye. This improvement was achieved without changing the optical characteristics of the eye. The results suggest that the aging brain retains enough plasticity to overcome the natural biological deterioration with age.

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.

Masking and crowding are major phenomena associated with contextual modulations, but the relationship between them remains unclear. We have recently shown that crowding is apparent in the fovea when the time available for processing is limited, pointing to the strong relationship between crowding in the spatial and temporal domains. Models of crowding emphasize the size (acuity) of the target and the spacing between the target and flankers as the main determinants that predict crowding. Our model, which is based on lateral interactions, posits that masking and crowding are related in the spatial and temporal domains at the fovea and periphery and that both can be explained by the increasing size of the human perceptive field (PF) with increasing eccentricity. We explored the relations between masking and crowding using letter identification and contrast detection by correlating the crowding effect with the estimated size of the PF and with masking under different spatiotemporal conditions. We found that there is a large variability in PF size and crowding effects across observers. Nevertheless, masking and crowding were both correlated with the estimated size of the PF in the fovea and periphery under a specific range of spatiotemporal parameters. Our results suggest that under certain conditions, crowding and masking share common neural mechanisms that underlie the spatiotemporal properties of these phenomena in both the fovea and periphery. These results could explain the transfer of training gains from spatiotemporal Gabor masking to letter acuity, reading, and reduced crowding.