D. L. Tomko

The relation between category and magnitude estimates of tactile intensity

Magnitude estimates of a wide intensive range of electrotactile stimuli were slotted against two category scales of the same stimuli. One scale was obtained with the usual narrow range of categories, the other with an expanded range derived from the numerical magnitude estimates. With the narrow range of categories, the function relating category ratings to magnitude estimates was surved concave downward as is usual. With the wide range of categories, the function was linear. Thus, the curvature previously ascribed to prothetic continua in general was found rather to result from a specific property of the response dimensions, i.e., from the restricted set of numbers made available as categories to the Ss.

Raesponses to head tilt in cat eighth nerve afferents

SummaryResponses to head tilt were recorded from eighth nerve axons in barbiturate anesthetized cats. The maximally excitatory head tilt (polarization vector), a zero-force discharge rate, and tilt sensitivity were measured for each cell. In one population of afferents, the maximum discharge frequency was obtained by aligning the saccular plane with gravity. The response properties of these saccular afferents were compared with a second population arising from the utriculus. Both the resting discharge rate and the response sensitivity were lower for saccular than utricular afferents in the cat. The average resting discharge was about 20% lower and the sensitivity about 15% higher in the cat than in the squirrel monkey.

Differences between cats in response properties of horizontal semicircular canal primary afferents

SummaryThe response properties of cat horizontal canal afferents (N = 81) were characterized by three parameters: their long time constants (τ), low frequency gain constants (G1), and middle frequency gain constants (Gm). An average value of each of these parameters was calculated for each of eight animals and comparisons were made across animals. There were significant differences between individual animals in their average values of τ and Gm. There was also a significant negative correlation between τs and Gms. An animal with a larger average τ tended to have a smaller average Gm. We also used anatomic data on membranous canal duct diameter from the literature to independently estimate the potential effect of interanimal anatomic variability on the predicted range of τ and Gm values in a population. We then compared the data from our 81 afferents with the predictions from the anatomic data.

Horizontal Canal Afferent Dynamics Measured Using White Noise and Cross Spectral Analysis

Research in vestibular receptor physiology has expanded significantly during the past decade, particularly in areas concerning aspects of information processing and control (3,6,12). The rapid development of system theory and control techniques for engineering applications has provided vestibular researchers with new ways of analyzing, describing, and classifying results from dynamic studies of this biologic control system. The use of computers for accurate stimulus control and data analysis has enabled use of experimental designs that would have been impractical only a decade ago. Our research in the cat semicircular canal afferent system was aided both theoretically and technically by use of certain control applications, programed via a laboratory computer system, as an integral part of the experimental design.

Analysis of Horizontal Canal Afferent Dynamics Using White Noise and Sinusoids in the Barbiturate Anesthetized Cat

Recent evidence has indicated that primary afferent neurons innervating a single semicircular canal can be subdivided into more than a single population on the basis of their dynamic response properties (6,11,14). Such variations in dynamic properties have been found to be correlated with neuronal variability (6,14), and thus indirectly with conduction velocity and axon diameter (7) or with the presumed anatomic locus in the crista of the receptors which the afferents innervate (2,11). It has been hypothesized that variations in first order afferent dynamic properties may be associated with their innervation patterns (5), or with local mechanical characteristics of the cupula near the innervated receptor cells (10).

Linear system analysis of cat semicircular canal afferent responses to angular acceleration.

HORIZONTAL canal first-order afferents in barbiturate-anesthetized cats were tested using white noise generated by three to ten periods (test protocols of three to five minutes) of pseudorandom binary sequences of rotational acceleration. Bandwidths spanned more than two decades and were centered near 0.1 Hz. Linear-system impulse responses were computed on line by cross-correlation and gain, and phase and coherence were computed via digital filtering and spectral analysis. Results were compared with those from velocity trapezoids and sinusoids in the same units.

System identification of semicircular canal afferent responses

A system identification analysis was used to obtain linear response characteristics from semicircular canal afferent spike trains. The responses were cross-correlated with pseudorandom binary sequences of rotational acceleration to obtain unit impulse responses in the time domain. Accurate linear system characteristics were obtained via cross-spectral transform and transfer function fitting techniques. The results imply that particular classes of semicircular canal afferents provide information concerning particular ranges of head movement dynamics for processing by central vestibular nuclei. These results are of interest for studying the transduction mechanisms of this receptor and determining its role as an information sensor for adaptive central control processes.