Increased emission intensity can compensate for the presence of noise in human click-based echolocation.

Echolocating bats adapt their emissions to succeed in noisy environments. In the present study we investigated if echolocating humans can detect a sound-reflecting surface in the presence of noise and if intensity of echolocation emissions (i.e. clicks) changes in a systematic pattern. We tested people who were blind and had experience in echolocation, as well as blind and sighted people who had no experience in echolocation prior to the study. We used an echo-detection paradigm where participants listened to binaural recordings of echolocation sounds (i.e. they did not make their own click emissions), and where intensity of emissions and echoes changed adaptively based on participant performance (intensity of echoes was yoked to intensity of emissions). We found that emission intensity had to systematically increase to compensate for weaker echoes relative to background noise. In fact, emission intensity increased so that spectral power of echoes exceeded spectral power of noise by 12 dB in 4-kHz and 5-kHz frequency bands. The effects were the same across all participant groups, suggesting that this effect occurs independently of long-time experience with echolocation. Our findings demonstrate for the first time that people can echolocate in the presence of noise and suggest that one potential strategy to deal with noise is to increase emission intensity to maintain signal-to-noise ratio of certain spectral components of the echoes.

Visual sensory stimulation interferes with people's ability to echolocate object size.

Echolocation is the ability to use sound-echoes to infer spatial information about the environment. People can echolocate for example by making mouth clicks. Previous research suggests that echolocation in blind people activates brain areas that process light in sighted people. Research has also shown that echolocation in blind people may replace vision for calibration of external space. In the current study we investigated if echolocation may also draw on 'visual' resources in the sighted brain. To this end, we paired a sensory interference paradigm with an echolocation task. We found that exposure to an uninformative visual stimulus (i.e. white light) while simultaneously echolocating significantly reduced participants' ability to accurately judge object size. In contrast, a tactile stimulus (i.e. vibration on the skin) did not lead to a significant change in performance (neither in sighted, nor blind echo expert participants). Furthermore, we found that the same visual stimulus did not affect performance in auditory control tasks that required detection of changes in sound intensity, sound frequency or sound location. The results suggest that processing of visual and echo-acoustic information draw on common neural resources.