Generalisation of learning with ITD discrimination across frequency and type of cue

Rowan, Daniel and Lutman, Mark E. (2005) Generalisation of learning with ITD discrimination across frequency and type of cue. 28th Annual Midwinter Research Meeting of the Association for Research in Otolaryngology, New Orleans, USA. 19 - 24 Feb 2005.

Abstract

A previous study¹ compared the ability of normal–hearing ‘naïve’ listeners to learn to discriminate low–frequency ongoing interaural time difference (ITD) or high–frequency interaural level difference (ILD), two important cues to localisation. The authors concluded that learning for ILDhad a longer time course and only partially transferred across frequency (~0.6 octaves), interpreted in the context of known differences in the processing of the two cues. Are differences in learning apparent with the discrimination of low–frequency ITD and high–frequency envelope–based ITD cues? We have addressed this using a 128–Hz tone and a 128–Hz tone ‘transposed’ to 4000 Hz; ITD sensitivity with these stimuli is comparable in highly trained listeners², thereby minimising a confounding effect of differential overall sensitivity when interpreting learning.Twenty naïve listeners were trained over 2160 trials with one or other stimulus or served as untrained controls. Performance was measured with both stimuli and sinusoidally amplitude modulated (SAM) tones during pre–and post–training sessions. ITD discrimination was measured using a 1–cue, 3–alternative forced–choice task and listeners were trained using a modified Levitt 2–down, 1–up adaptive procedure³. Overall, performance on pre–training was comparable for unmodulated and transposed stimuli but better than with SAM, although inter–individual variation was apparent. This reinforces the notion that ongoing ITD processing is functionally uniform across frequency. Both training groups learned more than untrained controls but the learning with either trained stimulus transferred entirely to the untrained stimuli. That is, learning generalised across both frequency (~5 octaves) and type of ITD cue. This generalisation may reflect commonality in the necessary listening strategies for optimal performance (e.g. detection of decorrelation) or the pooling across frequency in the underlying processing for ITD discrimination. This research was support by a grant from the Royal National Institute for Deaf People (RNID)
1 Wright BA, Fitzgerald MB. Proc Natl Acad Sci USA2001;98:12307–12
2 Bernstein LR, Trahiotis C. J Acoust Soc Am2002;112:1026–36
3 Trahiotis C, Bernstein LR, Buell TN, Spektor Z. J AcoustSoc Am 1990;87:1359-61

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