Audiovisual Association Learning in the Absence of Primary Visual Cortex.

Mehrdad Seirafi,Beatrice De Gelder,Peter De Weerd,Alan J Pegna

doi:10.3389/fnhum.2015.00686

Abstract

Learning audiovisual associations is mediated by the primary cortical areas; however, recent animal studies suggest that such learning can take place even in the absence of the primary visual cortex. Other studies have demonstrated the involvement of extra-geniculate pathways and especially the superior colliculus (SC) in audiovisual association learning. Here, we investigated such learning in a rare human patient with complete loss of the bilateral striate cortex. We carried out an implicit audiovisual association learning task with two different colors of red and purple (the latter color known to minimally activate the extra-genicular pathway). Interestingly, the patient learned the association between an auditory cue and a visual stimulus only when the unseen visual stimulus was red, but not when it was purple. The current study presents the first evidence showing the possibility of audiovisual association learning in humans with lesioned striate cortex. Furthermore, in line with animal studies, it supports an important role for the SC in audiovisual associative learning.

Highlights

There is strong evidence from neurophysiological animal experiments for the confluence of visual and auditory cues in superior colliculus (SC) (Jay and Sparks, 1984; Meredith and Stein, 1986; Alvarado et al, 2007; Yu et al, 2010)
The role of the geniculo-cortical pathway can be limited by ablating the striate cortex in animals. This has been done in the cat (Jiang et al, 2015), but due to the strong retino-genicular projections to extrastriate cortex (Rosenquist, 1985), it is difficult in such experiments to attribute audiovisual learning to extra-genicular pathways and, the SC
The present study is the first demonstrating the fast development of implicit audiovisual associations between consciously perceived auditory stimuli and visual stimuli that cannot be perceived because of complete bilateral striate lesion

Summary

INTRODUCTION

There is strong evidence from neurophysiological animal experiments for the confluence of visual and auditory cues in superior colliculus (SC) (Jay and Sparks, 1984; Meredith and Stein, 1986; Alvarado et al, 2007; Yu et al, 2010) This suggests a major role in audiovisual association-based learning. Because of the important role of the SC in audiovisual integration (Meredith and Stein, 1986), we hypothesized a contribution of SC in audiovisual association learning, which we believe to be exclusive for colored stimuli in medium-to-long wavelengths These ideas led us to test two predictions in a new implicit audiovisual association task, in which some auditory target stimuli were predictable on the basis of associated unseen visual information. That given the audio-visual integrative function of the SC, the cortically blind patient TN would acquire shortened reaction times (RT) to the visually predicted auditory targets, and, second, given the SC’s lack of sensitivity for short wavelengths (Marzi et al, 2009), that this RT advantage would be absent for visual stimuli that were colored purple

MATERIALS AND METHODS

RESULTS

Findings

DISCUSSION