The empirical characteristics of human pattern vision defy theoretically-driven expectations

Abstract

Contrast is the most fundamental property of images. Consequently, any comprehensive model of biological vision must incorporate this attribute and provide a veritable description of its impact on visual perception. Current theoretical and computational models predict that vision should modify its characteristics at low contrast: for example, it should become broader (more lowpass) to protect from noise, as often demonstrated by individual neurons. We find that the opposite is true for human discrimination of elementary image elements: vision becomes sharper, not broader, as contrast approaches threshold levels. Furthermore, it suffers from increased internal variability at low contrast and it transitions from a surprisingly linear regime at high contrast to a markedly nonlinear processing mode in the low-contrast range. These characteristics are hard-wired in that they happen on a single trial without memory or expectation. Overall, the empirical results urge caution when attempting to interpret human vision from the standpoint of optimality and related theoretical constructs. Direct measurements of this phenomenon indicate that the actual constraints derive from intrinsic architectural features, such as the co-existence of complex-cell-like and simple-cell-like components. Small circuits built around these elements can indeed account for the empirical results, but do not appear to operate in a manner that conforms to optimality even approximately. More generally, our results provide a compelling demonstration of how far we still are from securing an adequate computational account of the most basic operations carried out by human vision.

Emergence of crowding: The role of contrast and orientation salience

“…Such assumptions are not as parsimonious. Our findings of crowding only emerging after reliable orientation discrimination is established are consistent with models that posit a contribution of both simple and complex cells to mid-level vision ( Wilkinson, Wilson, & Ellemberg, 1997 ) and broadly consistent with a recent, mechanistic general model of human pattern perception that distinguishes between the operation of visual detectors under low and high-contrast constraints ( Neri, 2018 ).…”

Mechanisms of spectrotemporal modulation detection for normal- and hearing-impaired listeners

“…These simulations demonstrate that a simple MAX structure can, in principle, account for the complex pattern exposed by our measurements. Because the perceptual strategy engaged by listeners was strongly nonlinear, we cannot transparently interpret the filter estimates in terms of “perceptual weights” applied by listeners to different stimulus components (Neri, 2018b). As expected from theory (Neri, 2004; Tjan & Nandy, 2006; Neri, 2010b), simulated target-absent profiles closely resemble the model templates preceding the non-linear stage.…”

Mechanisms of Spectrotemporal Modulation Detection for Normal- and Hearing-Impaired Listeners

“…These observations support the view that our filter estimates reflect aspects of auditory processing that go beyond peripheral filtering and that the interindividual differences observed within both NH and HI populations reflect differential engagement of suprathreshold processes. These differences are unlikely due to differences in stimulus SNR or performance between individuals in the task, because filters derived from reverse correlation are most often insensitive to changes in SNR ( Neri, 2018b ). Different factors that we briefly discuss below could underlie this intragroup variability.…”