No abstract

This study examined the deleterious effects of a later-arriving sound on the processing of interaural differences of time (IDTs) from a preceding sound. A correlational analysis assessed the relative weight given to IDTs of source and echo clicks for echo delays of 1-64 ms when the echo click was attenuated relative to the source click (0-36 dB). Also measured were proportion correct and the proportion of responses predicted from the weights. The IDTs of source and echo clicks were selected independently from Gaussian distributions (mu=0 s, sigma = 100/s). Listeners were instructed to indicate the laterality of the source click. Equal weight was given to the source and echo clicks for echo delays of 64 ms with no echo attenuation. For echo delays of 16-64 ms, attenuating the echo had no substantial effect on source weight or proportion correct until the echo was attenuated by 18-30 dB. At echo delays < or =4 ms, source weights and proportions correct remained high regardless of echo attenuation. The proportions of responses predicted from the weights were lower at echo delays > or =16 ms. Results were discussed in terms of backward recognition masking and binaural sluggishness and compared to measurements of echo disturbance.

Auditory apparent movement was studied for source distance in depth varying in both relative and absolute distance. The stimuli consisted of 50-ms broadband noise pulses, each presented at an A-weighted sound-pressure level of 70 dB and at a fixed 0-deg azimuth. Aural targets (ATs) were separated into three distances ranging from 24 to 170 in. The time from onset (interstimulus onset interval or ISOI) of the stimuli varied from 6 to 150 ms. Results indicate that aural apparent movement is readily source displayed in depth (i.e., delta movement). As in studies with apparent movement in lateral dimensions, the relative timing of stimuli is crucial for the appearance of apparent movement [f(8,32)=8.16, p&lt;0.001]. The relative distance between speakers was also found to be a significant factor for the appearance of apparent movement [f(16,64)=3.66, p&lt;0.001]. These findings will be discussed further as they relate to previous research conducted on motion in the auditory system.

Minimum latencies required to locate and identify a visual target (visual search) were obtained in which the visual target could appear in a number of places on a depth plane (0-deg azimuth). A visual target was among the visual distracters located on a finite array segregated at three distances with placement of the target varied within the session from 24 to 232 in. from the subject. The stimulus was a broadband noise (70 dB A). Factoring in the distance of each speaker in relation to the subject, the inverse square law was considered in this paradigm. Four subjects were tested in three conditions: aurally aided search (spatially correlated), aurally unaided search (spatially uncorrelated, where no spatial information was provided), and unaided search (no auditory stimulus was used). The introduction of aurally aided search cues enhanced the ability to localize a target [f(38,84)=2.11, p&lt;0.005], thus lessening the workload on the visual system when distracters were in the visual field. Theoretical aspects and applications will be discussed further.