Abstract
BackgroundA small number of blind people are adept at echolocating silent objects simply by producing mouth clicks and listening to the returning echoes. Yet the neural architecture underlying this type of aid-free human echolocation has not been investigated. To tackle this question, we recruited echolocation experts, one early- and one late-blind, and measured functional brain activity in each of them while they listened to their own echolocation sounds.ResultsWhen we compared brain activity for sounds that contained both clicks and the returning echoes with brain activity for control sounds that did not contain the echoes, but were otherwise acoustically matched, we found activity in calcarine cortex in both individuals. Importantly, for the same comparison, we did not observe a difference in activity in auditory cortex. In the early-blind, but not the late-blind participant, we also found that the calcarine activity was greater for echoes reflected from surfaces located in contralateral space. Finally, in both individuals, we found activation in middle temporal and nearby cortical regions when they listened to echoes reflected from moving targets.ConclusionsThese findings suggest that processing of click-echoes recruits brain regions typically devoted to vision rather than audition in both early and late blind echolocation experts.
Highlights
Research has shown that people, like many animals, are capable of using reflected sound waves to perceive attributes of their silent physical environment
Validation of the Echolocation Stimuli To overcome the difficulties posed by studying echolocation in an MRI environment, a passive listening paradigm was adopted whereby the echolocation clicks and their echoes were pre-recorded in the listener’s ears (Figure 1D) and presented via fMRI compatible insert earphones (Figure 1E)
To test the validity of this paradigm, a direct behavioral comparison between active echolocation and passive listening was conducted using an angular position discrimination task, in which early blind participant (EB) and late blind participant (LB) discriminated the angular position of a test pole with respect to straight ahead (Figure 1B)
Summary
Research has shown that people, like many animals, are capable of using reflected sound waves (i.e. echoes) to perceive attributes of their silent physical environment (for reviews see [1,2,3]) This ability can been promoted through technological aids The enormous potential of this ‘natural’ echolocation ability is realized in a segment of the blind population that has learned to sense silent objects in the environment by generating clicks with their tongues and mouths and listening to the returning echoes [8]. The neural architecture underlying this type of aid-free human echolocation has not been investigated To tackle this question, we recruited echolocation experts, one early- and one late-blind, and measured functional brain activity in each of them while they listened to their own echolocation sounds
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