The Role of Visual Experience in Auditory Space Perception around the Legs.

It is widely accepted that vision plays a key role in the development of spatial skills of the other senses. Recent works have shown that blindness is often associated with auditory spatial deficits. The majority of previous studies have focused on understanding the representation of the upper frontal body space where vision and actions have a central role in mapping the space, however less research has investigated the back space and the space around the legs. Here we investigate space perception around the legs and the role of previous visual experience, by studying sighted and blind participants in an audio localization task (front-back discrimination). Participants judged if a sound was delivered in their frontal or back space. The results showed that blindfolded sighted participants were more accurate than blind participants in the frontal space. However, both groups were similarly accurate when auditory information was delivered in the back space. Blind individuals performed the task with similar accuracy for sounds delivered in the frontal and back space, while sighted people performed better in the frontal space. These results suggest that visual experience influences auditory spatial representations around the legs. Moreover, these results suggest that hearing and vision play different roles in different spaces

Binaural resolution.

The aim of the experiments described within this thesis was to measure binaural temporal and spectral resolution. Previous investigations that have studied temporal resolution (e.g. Bernstein et al., 2001) assumed that interfering noise dilutes delayed noise within the temporal window. The first two experiments described in this thesis have validated the dilution concept for correlated interfering noise, but not for uncorrelated interfering noise, the presence of which has a more detrimental effect than interfering correlated noise. The study by Bernstein et al. (2001) suggested that the equivalent rectangular bandwidth (ERD) of the binaural temporal window is considerably smaller than estimates made in previous studies (e.g. Kollmeier and Gilkey, 1990; Culling and Summerfield, 1998). The results from the experiments in this thesis disagree with those of Bernstein et al., and suggest that several factors led to their findings, including lack of control over the coherence of the stimulus due to the use of a detection task, the short duration of their stimuli, and the use of diotic interfering noise. The ERD of the binaural temporal window was found to range from 110-349 ms across listeners, a finding consistent with binaural sluggishness. In the frequency domain, a study by Sondhi and Guttman (1966) that investigated the frequency selectivity of the binaural system found evidence suggesting that binaural auditory filters are substantially wider than monaural auditory filters. Conversely, Kohlrausch (1988) measured auditory filters that were comparable to monaural filters. The results from the experiment conducted in this thesis found that binaural auditory filters are substantially wider than monaural auditory filters. Best fits were found to be 2-parameter asymmetric Gaussian filters with an ERB that ranged from 99-198 Hz at a centre frequency (CF) of 250 Hz, 138-215 Hz at a CF of 500 Hz, and 229-285 Hz at a CF of 750 Hz

Precision and accuracy of ocular following: influence of age and type of eye movement

Previous work on ocular-following emphasises the accuracy of tracking eye movements. However, a more complete understanding of oculomotor control should account for variable error as well. We identify two forms of precision: ‘shake’, occurring over shorter timescales; ‘drift’, occurring over longer timescales. We show how these can be computed across a series of eye movements (e.g. a sequence of slow-phases or collection of pursuit trials) and then measure accuracy and precision for younger and older observers executing different types of eye movement. Overall, we found older observers were less accurate over a range of stimulus speeds and less precise at faster eye speeds. Accuracy declined more steeply for reflexive eye movements and shake was independent of speed. In all other instances, the two measures of precision expanded non-linearly with mean eye speed. We also found that shake during fixation was similar to shake for reflexive eye movement. The results suggest that deliberate and reflexive eye movement do not share a common non-linearity or a common noise source. The relationship of our data to previous studies is discussed, as are the consequences of imprecise eye movement for models of oculomotor control and perception during eye movement