The role of spectral composition of sounds on the localization of sound sources by cats

Abstract

Sound localization along the azimuthal dimension depends on interaural time and level disparities, whereas localization in elevation depends on broadband power spectra resulting from the filtering properties of the head and pinnae. We trained cats with their heads unrestrained, using operant conditioning to indicate the apparent locations of sounds via gaze shift. Targets consisted of broadband (BB), high-pass (HP), or low-pass (LP) noise, tones from 0.5 to 14 kHz, and 1/6 octave narrow-band (NB) noise with center frequencies ranging from 6 to 16 kHz. For each sound type, localization performance was summarized by the slope of the regression relating actual gaze shift to desired gaze shift. Overall localization accuracy for BB noise was comparable in azimuth and in elevation but was markedly better in azimuth than in elevation for sounds with limited spectra. Gaze shifts to targets in azimuth were most accurate to BB, less accurate for HP, LP, and NB sounds, and considerably less accurate for tones. In elevation, cats were most accurate in localizing BB, somewhat less accurate to HP, and less yet to LP noise (although still with slopes ∼0.60), but they localized NB noise much worse and were unable to localize tones. Deterioration of localization as bandwidth narrows is consistent with the hypothesis that spectral information is critical for sound localization in elevation. For NB noise or tones in elevation, unlike humans, most cats did not have unique responses at different frequencies, and some appeared to respond with a "default" location at all frequencies.

Fig. 1.

Localization of long-duration broadband (BB), high-pass (HP), and low-pass (LP) noise targets. A: final gaze position (small open symbols) for stimuli presented from 12 target locations (corresponding large symbols) at (±45°, 0°), (±32°, 0°), (±18°, 0°), (±9°, 0°), (0°, 18°), (0°, 9°), (0°, −14°), and (0°, −23°). Central fixation LED is shown as +. B: accuracy of the vertical (gaze shift elevation, top) and horizontal (gaze shift azimuth, bottom) components of the saccades. Each point corresponds to a single trial. The motor error (abscissa) is the horizontal or vertical component of the distance between the initial gaze position on each trial and the actual position of the target. The gaze shift amplitude (ordinate) is the corresponding horizontal or vertical component of the response to that target position from the initial gaze position. Red line is the linear regression of saccade amplitude component and the motor error. Gain is the slope of the regression line and represents localization accuracy (gain = 1 corresponds to perfect localization accuracy); δ is the residual error after regression and is an indication of response precision or consistency; n is the number of trials. Data are from cat 18.

Fig. 2.

Localization of BB noise compared with narrow-band (NB) noise with center frequencies of 6, 8, 12, and 16 kHz for cat 17. Same format as Fig. 1. In A, targets in elevation (top) have been separated from targets in azimuth (bottom) for ease of presentation.

Fig. 3.

Localization accuracy improves for auditory noise targets as bandwidth increases. For targets in elevation, localization to HP noise is more accurate than that to LP noise. Response accuracy (gain) and associated 95% confidence intervals (see methods) for 2 cats (● and ○, cat 17; ■ and □, cat 18) are plotted as a function of type of bandwidth filtering.

Fig. 4.

Localization of BB noise (left) compared with tones of 1, 6, 10, and 14 kHz for cat G03. Same format as Fig. 2. In B, bottom row, the value b indicates the y-intercept of the regression line.

Fig. 5.

Response accuracy (gain) and associated 95% confidence intervals are plotted for BB noise and tone stimuli for 3 cats (▲, cat G03; ●, cat 21; ■, cat 28). A: cats vary in ability but are generally able to localize tones in azimuth. B: cats are unable to localize tones in elevation.

Fig. 6.

A: mean and SD of the final 2-dimensional gaze position for each of 8 tone frequencies (all targets in elevation combined) for 3 cats. B: mean and SD of final 2-dimensional gaze position for each of 4 NB noise targets (all targets in elevation combined) for 2 cats. Open symbols indicate spatial location of the target speakers.

Fig. 7.

A: latency of gaze saccades to BB noise and tone stimuli in azimuth. B: latency of gaze saccades to the same stimuli in elevation. The short red lines indicate the mean latency at each condition.