Auditory localization in primates as a function of stimulus bandwidth

Abstract

Monkeys (Macaca) were trained by operant conditioning techniques to report the minimum discriminable change in the locus of a sound in space. When a monkey made contact with the response key, a pulsed acoustic stimulus was presented from a standard location (zero degrees azimuth). After a variable number of pulses the stimulus changed position from the standard to one of several comparison locations. If the monkey reported this change by releasing the key, it received food as reinforcement. Thresholds for the minimum discriminable change in locus of a sound were determined by the method of constant stimuli. Testing was conducted under free-field conditions in an anechoic chamber. Monkeys were tested with noise bands of various bandwidths. The results indicate an inverse relation between threshold and bandwidth; as bandwidth is decreased the threshold for detection of a change in acoustic locus is increased. [This research was supported by a grant from NSF.]

The Control of Responding by Sounds: Unusual Effect of Reinforcement

“…For example, the ability of rats and monkeys readily to discriminate the position of sounds is a function of the complexity of the spectral content of the sound (Beecher & Harrison, 1971;Brown, Beecher, Moody, & Stebbins, 1975;Harrison & Beecher, 1969;Harrison & Briggs, 1977), and of the relative positions of the sound source and response sites (Downey & Harrison, 1972Harrison, Downey, Segal, & Howe, 1971;Harrison, Iversen, & Pratt, 1977). White noise is more salient than a pure tone (Segal & Harrison, 1978), and hedgehogs, in contrast to cats and tree shrews, cannot discriminate the position of a pure tone below about 15 kHz, although such sounds are well within their range of hearing (Masterton, Thompson, Bechtold, & Robards, 1975;Ravizza, Heffner, & Masterton, 1969).…”

Alarm Calls of California Ground Squirrels (Spermophilus beecheyi)

“…The differences in receiver response profiles between whistle and chatter-chat situations parallel those exhibited by passerine birds in response to aerial predator calls and mobbing vocalizations (MARLER and I~AMILTON 1967). Although the structural differences between whistles and chatter-chats do not precisely parallel those described by MARLER, e. g., whistles are not pure tones, recent psychophysical data and theory suggest that whistles and chatter-chats should differ in localizability (BROWN 1976). We tested this hypothesis with a single human subject by comparing the mean error of location of the two calls depicted in Fig.…”

Sensory Function in Animals

“…The method of constant stimuli is illustrated in a series of experiments in which monkeys were trained through operant conditioning procedures to report a change in the horizontal coordinate (azimuth) of a sound in space (7,8). The animals were required to perform an observing response by making contact with a response disk, which resulted in the delivery of a series of tone pulses from a reference speaker located directly ahead.…”

“…Equally important, requiring an observing response can help to guarantee a replicable position of the sensory end organ relative to the stimulus transducer. The observing response of holding or contacting a response disk renders the subject silent and motionless-a condition conducive to, for example, stable audiometric testing (7,35,39,56). The optimal observing response may be specific for each animal and sensory modality under investigation.…”