Auditory cortex lesions and interaural intensity and phase-angle discrimination in cats

Abstract

1. A currently unresolved question concerning the effects of auditory decortication on sound localization is whether or not operated animals have a normal capacity for discriminating the small interaural differences in phase angle or intensity that result from the spatial separation of sound sources relative to the head. The present experiment was designed to provide data relevant to this question. 2. Four normal and three operated cats (bilateral ablations of AI, AII Ep, SII, I-T), wearing stereo headsets, were tested with an active avoidance procedure to detect reversals in the interaural phase-angle or intensity relations of binaural 1-kHz tones. For both groups of cats, the detection thresholds for interaural intensity and phase angle were found to be close to 1 dB and 5 degrees, respectively. 3. In addition, we found that both unoperated and operated cats exhibited positive transfer from the original lateralization task involving the detection of interaural reversals of phase angle or intensity to a new test, which required the cats to identify, in an absolute sense, which ear received the leading or louder signals. 4. Thus, the present investigation provides additional evidence that the neocortex has no primary sensory role in sound localization.

Detection versus discrimination of brief tones by cats with auditory cortex lesions

“…The auditory cortex lesions of the present series of cats were quite comparable to those repo.rted in the Cranford and Igarashi (1977) in frequency. The tests with 100-ms duration signals revealed no significant differences in the magnitude of the difference limens between the unoperated and operated cats.…”

“…In contrast to the Russian findings, the present author recently reported evidence (Cranford and Igarashi, 1977) that cats with large bilateral auditory cortex lesions are unimpaired in their ability to detect either Cats were initially trained to detect a change from either 1 to 1.2 kHz (cats 5582, 5691, 7263, 7710, 9046) or from 1 to 0.8 kHz (cat 8521). After mastering the discrimination with 500-ms duration tones (i.e., achieving a criterion score of 11/12 correct during one session), the tonal durations were reduced over days to a value of 100 ms.…”

“…(1967), are especially interesting. When, the author (Cranford and Igarashi, 1977) failed to replicate, with the cat, the Russian report that dogs and humans with auditory cortex lesions exhibit significant elevations of their absolute thresholds for brief sounds, we suggested the possibility that procedural variables might have been the basis for the discrepancy. In contrast to our procedure of presenting sounds from overhead free-field speakers, the Russians tested each of the two ears of individual subjects with headphones.…”

Connections of cat auditory cortex: II. Commissural system

“…In the cat, callosal fiber transection (Moore et al, 1974), cortical ablations (Neff and Casseday, 1977;Cranford, 1979), electrophysiology (Stecker et al, 2005), and cooling inactivation (Malhotra et al, 2004) each demonstrate interhemispheric roles for AC areas in sound location that are not restricted to AI (Jenkins and Merzenich, 1984). Perhaps the physiology of an area differs between hemispheres, as studies of right hemisphere commissural dominance imply (Bianki et al, 1988).…”

Role of cat primary auditory cortex for sound-localization behavior

“…Thus, by this view, animals with cortical lesions are incapable of making the complex motor responses necessary for free-field localization tests of the type employed in these studies but may be capable of indicating the locus of a sound by making simple lever presses (29) or by making reflexive or orienting responses (5, 8 1, 83). This conclusion is based, in part, on the observation that cats with cortical lesions retain the ability to detect interaural intensity and phase differences, and it thus provides additional evidence that the neocortex has no primary sensory role in sound localization (18). However, these studies by no means provide a proof that these cats have a normal perception of sound space.…”