Auditory motion processing after early blindness

Studies showing that occipital cortex responds to auditory and tactile stimuli after early blindness are often interpreted as demonstrating that early blind subjects ‘see’ auditory and tactile stimuli. One such example is that area hMT+ – a region associated with visual motion processing in sighted – responds to auditory and tactile motion stimuli within early blind individuals. However, to claim that blind subjects ‘see’ using occipital cortex requires that occipital responses directly mediate the perception of auditory stimuli, rather than simply modulating or augmenting responses within auditory areas. We show that occipital responses to auditory motion after early blindness are associated with subjects’ decisions about auditory motion and provide evidence that blind individuals do indeed ‘see’ auditory motion.

HFSP Long-Term Fellow Fang Jiang and colleagues
authored on Fri, 20 February 2015

To identify regions associated with the conscious experience of auditory motion we dissociated neuronal responses associated with the perceptual experience of motion from the physical presence of motion in the display by asking observers to report the perceived direction of an ambiguous stimulus. Both coherent and ambiguous motion stimuli were defined using a combination of inter-aural time differences, inter-aural level differences, and Doppler shift that simulated an auditory stimulus traveling along a fronto-parallel plane.  No net motion was applied in the ambiguous motion stimulus.

Using fMRI pattern classification, we found that in sighted individuals the perceived direction of motion for both coherent and ambiguous auditory motion stimuli was accurately categorized based on neural responses within auditory cortex (specifically the right planum temporale and lateral occipital cortex). In contrast, within early blind individuals auditory motion decisions were only successfully categorized based on responses within hMT+, and could not be categorized based on responses within either the planum temporale or lateral occipital cortex. This double dissociation demonstrates firstly that early blind responses to auditory motion within MT+ are associated with the perception of auditory motion, and secondly that these responses do indeed supplant rather than augment the role of auditory cortex in auditory motion perception. Blind individuals do indeed ‘see’ auditory motion.

Reference

Auditory motion processing after early blindness. Journal of Vision. Jiang, F., Stecker, G.C., Fine, I. Journal of Vision (2014) 14(13):4, 1-18.

Link to Journal of Vision article

Pubmed link