Strength of early visual adaptation depends on visual awareness

Abstract

We measured visual-adaptation strength under variations in visual awareness by manipulating phenomenal invisibility of adapting stimuli using binocular rivalry and visual crowding. Results showed that the threshold-elevation aftereffect and the translational motion aftereffect were reduced substantially during binocular rivalry and crowding. Importantly, aftereffect reduction was correlated with the proportion of time that the adapting stimulus was removed from visual awareness. These findings indicate that the neural events that underlie both rivalry and crowding are inaugurated at an early stage of visual processing, because both the threshold-elevation aftereffect and translational motion aftereffect arise, at least in part, from adaptation at the earliest stages of cortical processing. Also, our findings make it necessary to reinterpret previous studies whose results were construed as psychophysical evidence against the direct role of neurons in the primary visual cortex in visual awareness. binocular rivalry ͉ crowding ͉ vision V isual adaptation has been dubbed the psychologist's microelectrode (1) because the resulting visual aftereffects presumably reveal response properties of neural mechanisms that are activated by adapting stimuli. Also, measuring visual adaptation under visual conditions that render the adapting stimulus invisible allows one to draw inferences about the neural concomitants of the conditions that produce stimulus invisibility. Specifically, a result showing a full-strength aftereffect that is generated by an invisible stimulus implies normal, unperturbed neural activation at the site of adaptation. This outcome implies that the neural correlates of the visual phenomenon that are used to render the adapting stimulus invisible lie beyond the neural mechanisms that are responsible for the aftereffect. This line of reasoning has been applied to the study of binocular rivalry and visual crowding, which are two extensively studied visual phenomena that are used to ''erase'' visual stimuli from awareness (2). The results have shown that full-strength pattern and motion aftereffects (MAEs) can be induced even when the high-contrast inducing stimuli were absent from awareness for a substantial portion of the adaptation period during binocular rivalry (3-7) and crowding (8, 9). Because adaptation producing these aftereffects includes neural events that presumably occur within cortical areas ranging from the primary visual cortex (V1) (10-12) to the middle-temporal visual area (12, 13), these psychophysical findings have reasonably been interpreted as evidence for the high-level origin of both rivalry (14, 15) and crowding (8,14). Also, these same results were regarded by some workers as key psychophysical evidence against the direct involvement of V1 neurons in conscious visual awareness (16)(17)(18)(19). Measurement of full-strength aftereffects under conditions of rivalry and crowding shows a clear dissociation between the abolished perceptual awareness of the adapting stimulus and unperturbe...

Melodic sound enhances visual awareness of congruent musical notes, but only if you can read music

“…After all, in other circumstances suppression durations of a visual stimulus are impacted by the properties of that stimulus, including its physical characteristics (9), its configural properties (30,66), its affective connotation (67,68), its lexical familiarity (32), and its social connotation (69). However, in all these instances the features defining the suppressed stimulus are plausibly being registered and remain available for analysis (70), albeit with reduced fidelity or signal strength (34). There is no reason why this should not be true for the visual features-contour size, orientation and contrast polarity-comprising notes contained in the musical scores used as a rival stimulus in our experiments.…”

Temporal structure coding with and without awareness

“…Furthermore, all the adaptation effects we found in the visible condition were independent of motion strength (i.e., ISI for apparent motion, and walking speed for biological motion), and adaptation to apparent motion was constant despite the linear decrease in the subjective motion strength. The fact that adaptation does not decrease with motion strength is probably due to the existence of a compressive nonlinearity, with adaptation response saturating at high motion strength (Blake, Tadin, Sobel, Raissian, & Chong, 2006). Similarly, the fact that adaptation to visible and invisible apparent motion was of similar amplitude at high motion strength (i.e., ISI = 100 ms) is likely due to response saturation, which in this case would conceal the decrease of sensitivity under CFS (the saturation of adaptation responses is unlikely in case of biological motion, since the effect amplitude differed between the visible and invisible condition).…”

The effect of spatial attention on invisible stimuli

“…To completely suppress the adaptors, dynamic radial gratings were used as suppressors, alternating between clockwise and counterclockwise rotation at 1 Hz. These suppressors do not produce motion-or orientation-specific aftereffects (Blake et al, 2006). Two sinusoidal gratings (adaptors) were presented to the left and the right visual field of the nondominant eye, and two radial gratings (suppressors) were presented to the left and the right visual fields of the dominant eye.…”

“…Postadaptation contrast measurements, with exactly the same procedure as the baseline-contrast threshold measurements (except that now the number of trials was fixed), were interleaved with top-up adaptation periods. We did not use different orientations for the test stimuli, since a previous study with a similar method had shown this aftereffect was orientation specific (Blake et al, 2006).…”