Darks Are Processed Faster Than Lights

Abstract

Recent physiological studies claim that Dark stimuli have access to greater neuronal resources than Light stimuli in early visual pathway. We used two sets of novel stimuli to examine the functional consequences of this Dark dominance in human observers. We show that increment and decrement thresholds are equal when controlled for adaptation and eye-movements. However, measurements for salience differences at high-contrasts show that Darks are detected pronouncedly faster and more accurately than Lights when presented against uniform binary noise. In addition, the salience advantage for Darks is abolished when the background distribution is adjusted to control for the irradiation illusion. The threshold equality suggests that the highest sensitivities of neurons in the ON and OFF channels are similar, whereas the salience difference is consistent with a population advantage for the OFF system.

Neuronal nonlinearity explains greater visual spatial resolution for darks than lights

“…Furthermore, we show that the background luminance affects more ON than OFF channels in their response magnitude, response linearity, and receptive field size. Finally, we show that changes in the ON channel with background luminance can explain the dynamics of the irradiation illusion: The illusion is perceived stronger on dark/light backgrounds than on gray backgrounds (7).…”

“…Galilei (4) related the difference in resolution to the observation that a light patch on a dark background appears larger than the same sized dark patch on a light background, an illusion that von Helmholtz (5) named the "irradiation illusion." Although this illusion has been studied in the past (6,7), its underlying neuronal mechanisms remain unknown. It has been suggested that the perceived size differences could be caused by the light scatter in the optics of the eye followed by a neuronal nonlinearity (6,7), but there are no neuronal measurements of a nonlinearity that fits the explanation.…”

“…Although this illusion has been studied in the past (6,7), its underlying neuronal mechanisms remain unknown. It has been suggested that the perceived size differences could be caused by the light scatter in the optics of the eye followed by a neuronal nonlinearity (6,7), but there are no neuronal measurements of a nonlinearity that fits the explanation. Previous studies revealed differences in response linearity between ON and OFF retinal ganglion cells (8,9) and horizontal cells (10).…”

Binocular functional architecture for detection of contrast-modulated gratings

“…Such asymmetries in response to contrast polarity probably have their origin in an early compressive response to luminance, perhaps driven by local light adaptation at the photoreceptor level. Such a nonlinearity gives rise to polarity asymmetries in a great variety of perceptual outcomes (Lu & Sperling, 2012), including perceived size and perceived location of edges (Georgeson & Freeman, 1997;Mather & Morgan, 1986), and reaction times (Komban, Alonso, & Zaidi, 2011). It is also reflected in neural responses at the retinal, lateral geniculate and cortical levels (Kremkow et al, 2014).…”

Cortical brightness adaptation when darkness and brightness produce different dynamical states in the visual cortex

“…This finding is quite different from those in several previous studies that reported a general increase of response amplitude without changes of dynamics in V1 responses to small black vs. white stimuli. For instance, investigations of the visual cortex of human (20,34,35), monkey (8,17), and cat (36,37) reported an increase of response gain for small black targets but no change in response dynamics. Two possibilities might explain why our results on V1 dynamical states were not found in earlier experiments.…”