Sound-Localization Performance in the Cat: The Effect of Restraining the Head

Abstract

In oculomotor research, there are two common methods by which the apparent location of visual and/or auditory targets are measured, saccadic eye movements with the head restrained and gaze shifts (combined saccades and head movements) with the head unrestrained. Because cats have a small oculomotor range (approximately Ϯ25°), head movements are necessary when orienting to targets at the extremes of or outside this range. Here we tested the hypothesis that the accuracy of localizing auditory and visual targets using more ethologically natural head-unrestrained gaze shifts would be superior to head-restrained eye saccades. The effect of stimulus duration on localization accuracy was also investigated. Three cats were trained using operant conditioning with their heads initially restrained to indicate the location of auditory and visual targets via eye position. Long-duration visual targets were localized accurately with little error, but the locations of short-duration visual and both long-and short-duration auditory targets were markedly underestimated. With the head unrestrained, localization accuracy improved substantially for all stimuli and all durations. While the improvement for longduration stimuli with the head unrestrained might be expected given that dynamic sensory cues were available during the gaze shifts and the lack of a memory component, surprisingly, the improvement was greatest for the auditory and visual stimuli with the shortest durations, where the stimuli were extinguished prior to the onset of the eye or head movement. The underestimation of auditory targets with the head restrained is explained in terms of the unnatural sensorimotor conditions that likely result during head restraint.

Specialization for Sound Localization in Fields A1, DZ, and PAF of Cat Auditory Cortex

“…Our analysis was limited by use of ensembles of no more than 16 units and by use of 20°spatial bins. Given those limitations, it is remarkable that the smallest errors in our estimates averaged within a factor of two of errors in cats' behavioral localization judgments (e.g., May and Huang, 1996;Tollin et al, 2005). We assume that the superior accuracy observed in localization behavior reflects the activity of more than 16 neurons and probably involves a more optimal analysis of temporal firing patterns than the simple three-time point pattern recognition scheme that we devised.…”

“…These observations suggest that PAF might have a principal role in sound localization. A difficulty with that argument is that populations of PAF neurons show their greatest location signaling accuracy for lateral regions of space, whereas psychophysical localization accuracy in cats (May and Huang, 1996;Tollin et al, 2005) and humans (e.g., Makous and Middlebrooks, 1990;Carlile et al, 1997) is greatest around the frontal midline. It might be that PAF scans regions that are remote from frontal attention, cooperating with another cortical field, such as DZ, to provide highacuity localization near the midline.…”

Localization of Click Trains and Speech by Cats: the Negative Level Effect

“…Horizontal and vertical gaze positions were determined separately by a velocity criterion (Populin and Yin 1998;Tollin et al 2005). The beginning of the gaze movement was marked as the point in time when steady fixation ended, i.e., when the magnitude of the velocity exceeded 2 standard deviations (SDs) of the mean velocity (near zero) computed during the initial steady fixation.…”

“…The localization performance was measured by comparing the actual gaze shift with the motor error (see Tollin et al 2005 for details). The motor error was the difference between the target-in-space position and initial gaze positions at the time when the target was turned on (Fig.…”

“…1B, straight lines). Sound localization accuracy was measured by the slope of the function, which was referred to as the gain (Tollin et al 2005). A gain of 1.0 indicates that, on average across all trials and target positions, the cat locates the targets to actual positions, while gains G1.0 indicate that target locations are underestimated.…”