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

The frequency with which blinded mottled sculpin, Cottus bairdi, oriented t owards a dipole current source (50-Hz vibrating sphere) was measured as a f unction of source distance (2-18 cm) and azimuth (either 0 degrees in front or 90 degrees to the side of the fish). The orienting frequency declined f rom over 70% to under 50% as source distance increased from 4 to 12 cm for both frontal and lateral sources. When response biases (frequency of respon ding in the absence of the signal) were taken into account with the perform ance metric d', threshold distances (distances at which d' fell to 1) for f rontal (12.5 cm) and lateral (11.6 cm) sources were 1.35-1.45 times the mea n standard length of fish used in this study. At distances less than 8 cm, d' values were considerably higher (i.e. performance was better) for the la teral source, despite the fact that peak stimulus levels at the fish were t wice as high for frontal as for lateral sources at any given distance, Perf ormance differences may be related to differences in spatial excitation pat terns, in particular the distribution of opposing pressure gradient directi ons along the lateral-line system, present for lateral sources, but absent for frontal sources. (C) 1999 The Association for the Study of Animal Behav iour.