Sampling without Vision: Auditory Performance Fluctuates in Congenitally Blind Individuals

In the past decade, studies have shown that attention fluctuates at ∼8 Hz, alternating between intervals of increased and decreased visual performance. This modulation of performance, which has been observed primarily in the visual modality, also manifests in behavior and has been termed “attentional sampling.” In this study, we investigate whether sampling goes beyond vision and serves as a domain general mechanism shared by other perceptual systems. Specifically, we examined the auditory modality, in which there is contradicting evidence for endogenous sampling at similar frequencies. Additionally, we sought to investigate a putative role for visual experience in sampling in audition. To this end, sighted, sighted blindfolded, individuals with acquired blindness, and individuals with congenital blindness (n = 12) detected a brief target (an intensity decrement) within an ongoing white noise stimulus. We observed 8- to 10-Hz sampling in the congenitally blind group only. We discuss this finding within the context of two possible, and even compatible, accounts. The first is that a lack of early visual experience in the congenitally blind drives the recruitment of “visual” cortices for auditory inputs, resulting in attentional sampling dynamics (typically observed in vision) in audition. The second is that auditory sampling exists in the sighted brain but is either obscured by visual inputs and other reflexive visual processes, or might unfold at an entirely different rhythm. In fact, the acquired blind and the two sighted samples exhibited a significant low frequency fluctuation at 2 Hz in their auditory performance. Although this study was not designed to investigate sampling at such low frequencies, this finding is consistent with a role for delta-band activity in audition as well as in temporal expectation mechanisms. In order to further substantiate a role for delta band sampling, it would be important to design paradigms better suited to study lower frequencies in behavior, both in sighted individuals and under different degrees of visual input processing.