Signal detection theory, lateral-line excitation patterns and prey capture behaviour of mottled sculpin

Abstract

The frequency with which blinded mottled sculpin, Cottus bairdi, oriented towards a dipole current source (50-Hz vibrating sphere) was measured as a function of source distance (2–18cm) and azimuth (either 0° in front or 90° to the side of the fish). The orienting frequency declined from over 70% to under 50% as source distance increased from 4 to 12cm for both frontal and lateral sources. When response biases (frequency of responding in the absence of the signal) were taken into account with the performance metric d′, threshold distances (distances at which d′ fell to 1) for frontal (12.5cm) and lateral (11.6cm) sources were 1.35–1.45 times the mean standard length of fish used in this study. At distances less than 8cm, d′ values were considerably higher (i.e. performance was better) for the lateral source, despite the fact that peak stimulus levels at the fish were twice as high for frontal as for lateral sources at any given distance. Performance differences may be related to differences in spatial excitation patterns, in particular the distribution of opposing pressure gradient directions along the lateral-line system, present for lateral sources, but absent for frontal sources.