Perceptual constancy with a novel sensory skill

Changes in primary visual and auditory cortex of blind and sighted adults following 10 weeks of click-based echolocation training

Recent work suggests that the adult human brain is very adaptable when it comes to sensory processing. In this context, it has also been suggested that structural "blueprints" may fundamentally constrain neuroplastic change, e.g. in response to sensory deprivation. Here, we trained 12 blind participants and 14 sighted participants in echolocation over a 10-week period, and used MRI in a pre-post design to measure functional and structural brain changes. We found that blind participants and sighted participants together showed a training-induced increase in activation in left and right V1 in response to echoes, a finding difficult to reconcile with the view that sensory cortex is strictly organized by modality. Further, blind participants and sighted participants showed a training induced increase in activation in right A1 in response to sounds per se (i.e. not echo-specific), and this was accompanied by an increase in gray matter density in right A1 in blind participants and in adjacent acoustic areas in sighted participants. The similarity in functional results between sighted participants and blind participants is consistent with the idea that reorganization may be governed by similar principles in the two groups, yet our structural analyses also showed differences between the groups suggesting that a more nuanced view may be required.

Effects of type of emission and masking sound, and their spatial correspondence, on blind and sighted people's ability to echolocate

Ambient sound can mask acoustic signals. The current study addressed how echolocation in people is affected by masking sound, and the role played by type of sound and spatial (i.e. binaural) similarity. We also investigated the role played by blindness and long-term experience with echolocation, by testing echolocation experts, as well as blind and sighted people new to echolocation. Results were obtained in two echolocation tasks where participants listened to binaural recordings of echolocation and masking sounds, and either localized echoes in azimuth or discriminated echo audibility. Echolocation and masking sounds could be either clicks or broad band noise. An adaptive staircase method was used to adjust signal-to-noise ratios (SNRs) based on participants' responses. When target and masker had the same binaural cues (i.e. both were monoaural sounds), people performed better (i.e. had lower SNRs) when target and masker used different types of sound (e.g. clicks in noise-masker or noise in clicks-masker), as compared to when target and masker used the same type of sound (e.g. clicks in click-, or noise in noise-masker). A very different pattern of results was observed when masker and target differed in their binaural cues, in which case people always performed better when clicks were the masker, regardless of type of emission used. Further, direct comparison between conditions with and without binaural difference revealed binaural release from masking only when clicks were used as emissions and masker, but not otherwise (i.e. when noise was used as masker or emission). This suggests that echolocation with clicks or noise may differ in their sensitivity to binaural cues. We observed the same pattern of results for echolocation experts, and blind and sighted people new to echolocation, suggesting a limited role played by long-term experience or blindness. In addition to generating novel predictions for future work, the findings also inform instruction in echolocation for people who are blind or sighted.