Neural Correlates of Natural Human Echolocation in Early and Late Blind Echolocation Experts

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.

Correlation between vividness of visual imagery and echolocation ability in sighted, echo-naïve people

“…In agreement with this idea Ashmead et al (1998) provided a model and measurements of ambient sound fields suggesting that variations in frequency bands of 500 Hz or below are informative during a locomotion task that requires participants to listen to acoustic reverberations arising from their own foot-steps while walking. Importantly, in our current task, participants made mouth clicks which have considerable energy in higher frequency bands (Rojas et al 2009;Thaler et al 2011). Yet, we replicated Carlson-Smith and Wiener's (1996) results with regard to the positive relationship between performance on the DCI test at 500 Hz and echolocation, and the lack of a statistical relationship between performance on DCI and DFM test for 2000 Hz.…”

“…In a recent fMRI study investigating the neural correlates of echolocation in people, it was found that the calcarine cortex (CC), i.e. early 'visual' cortex, of blind echolocation experts was more active during the processing of echo sounds as compared to the processing of echo-less control sounds (Thaler et al 2011). The same study also found that there was no differential activity in auditory cortex.…”

“…On a purely physical basis, information about these properties is carried through mono-and binaural variations in echo timing, spectrum (pitch) and intensity (loudness), and people may be able to exploit these variables for echolocation (Cotzin and Dallenbach 1950;Papadopoulos et al 2011;Rosenblum et al 2000;Schenkman and Nilsson 2010;Stoffregen and Pittenger 1995), though the use of one or the other acoustic variable may also depend on the echolocation task people engage in. Remarkably, some expert echolocators are even able to perform accurate object identification using echolocation (Thaler et al 2011), but the information underlying this skill is unclear to date. Echolocation may have real-life advantages for blind people (Thaler 2013b).…”

The role of head movements in the discrimination of 2-D shape by blind echolocation experts

“…Similarly, some blind humans have developed the ability to use echoes from self-produced sounds to perceive their silent surroundings. For example, blind echolocators can perceive information such as the size, shape, distance, motion, and material properties of silent objects Kellogg, 1962;Rice, 1967;Rice, 1969;Rice, Feinstein, & Schusterman, 1965;Schenkman & Nilsson, 2010;Stoffregen & Pittenger, 1995;Teng, Puri, & Whitney, 2011;Thaler, Arnott, & Goodale, 2011;). In this way, then, echolocation could be considered a crude substitute for vision, allowing blind humans to perceive aspects of their environment that would otherwise go undetected.…”

Experimental evaluation of binaural recording system using a miniature dummy head

“…For example, one study examined the ability of blind subjects to identify the presence of an obstacle by making click sounds and listening to the echoes [2,3]. Other studies examined target detection when blind subjects listened to echoes from a target using a loudspeaker that produced artificial sounds [4,5]. Furthermore, a mobility aid for blind people was developed that used digital signal processing to convert ultrasound echoes from a target into audible sounds in real time [6].…”