Perception of dysphonic voice quality by naive listeners.

For clinical assessment as well as student training, there is a need for information pertaining to the perceptual dimensions of dysphonic voice. To this end, 24 naive listeners judged the similarity of 10 female and 10 male vowel samples, selected from within a narrow range of fundamental frequencies. Most of the perceptual variance for both sets of voices was associated with "degree of abnormality" as reflected by perceptual ratings as well as combined acoustic measures, based upon filtered and unfiltered signals. A second perceptual dimension for female voices was associated with high frequency noise as reflected by two acoustic measures: breathiness index (BRI) and a high-frequency power ratio. A second perceptual dimension for male voices was associated with a breathy-overtight continuum as reflected by period deviation (PDdev) and perceptual ratings of breathiness. Results are discussed in terms of perceptual training and the clinical assessment of pathological voices.

Simulation of motion on the skin. V. Effect of stimulus temporal frequency on the representation of moving bar patterns in primary somatosensory cortex of monkeys.

1. To assess the mechanisms used by cortical neurons to sense motion across the skin, we applied pulsatile stimuli to a series of adjacent positions on the glabrous skin of the hand using a computer-controlled OPTACON stimulator. We describe responses of 129 single neurons in primary somatosensory cortex of alert monkeys to a horizontal bar pattern that was displaced proximally or distally in 1.2-mm steps at 10-, 20-, and 40-ms intervals (100, 50, and 25 Hz, respectively). These frequencies span the range in which apparent motion is transformed perceptually in humans from a smooth uninterrupted sweep into a series of distinct pulses that are resolved as separate events. The experiments are thus designed to decipher the neural correlates distinguishing continuous motion from discrete taps. 2. Cortical receptive fields mapped with moving bar patterns spanned 5-24 rows on the tactile array (16.2 +/- 5.4, mean +/- SD). Over 40% of the fields encompassed 18 or more rows (greater than or equal to 21.6 mm), allowing these neurons to integrate spatial information from an entire image displayed on the OPTACON. Cortical receptive fields are considerably larger than those of mechanoreceptors mapped with the same moving bar patterns (4.2 +/- 2.3 rows, mean +/- SD), reflecting convergent inputs in subcortical and cortical relays. Responses were either relatively uniform across the field or strongest at the initial point of entry, depending on the frequency of stimulation. A sharply defined field center was absent from most of the cells recorded in this study. 3. Temporal frequency of stimulation appears to be a major determinant of cortical firing patterns. Low-frequency stimuli are more effective in activating cortical neurons, producing more spikes per sweep and greater phase-locking to individual stimuli than do high frequencies. The total spike output of cortical neurons is proportional to the pulse interval over the range 10-40 ms, increasing linearly by an average of 5.9 spikes/10-ms increase in pulse period. Peak firing rates and modulation amplitude are also highest when pulses are presented at long intervals, falling significantly as the stimulation frequency rises. The reduction in firing at high pulse rates is apparently due to central mechanisms, as both rapidly adapting and Pacinian corpuscle afferents display nearly constant spike outputs and uniform sensitivity within the field when tested with identical bar patterns. Central networks thus behave as low-pass filters, reducing cortical responses to rapidly applied sequential stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Tizanidine-induced depression of polysynaptic cutaneous reflexes in nonanesthetized monkeys is mediated by an alpha 2-adrenergic mechanism.

Previous studies in anesthetized or reduced preparations of nonprimate animals revealed that the alpha 2-adrenergic agonist tizanidine, clinically used as an antispastic drug, effectively reduces polysynaptic flexor reflexes. To further clarify the invoked adrenergic mechanism for physiological motor functions, and in view of the clinical relevance of tizanidine, the effect of this substance was reinvestigated in awake, nonanesthetized monkeys. Systemic applications of tizanidine dose-dependently reduced the magnitude of the electromyographic response of the flexor reflex that was induced by nonnoxious stimulation of cutaneous afferents. Whereas the effects on the flexor response were consistent, the changes of the background electromyogram were much more variable, often not paralleling those of the reflex. The reflex depression produced by tizanidine could be prevented by pretreatment with the alpha 2-antagonist yohimbine. It is concluded that the action of tizanidine on spinal reflexes, and therefore probably also on hyperactive reflexes of spastic patients, is mediated via the alpha 2-adrenergic properties of the drug. On the basis of the present results, taken together with previous observations that tizanidine transiently inactivates neurons of the nucleus locus coeruleus, it is proposed that the reflex depression may be caused by a removal of a descending noradrenergic facilitation exerted on spinal reflex transmission. This interpretation leaves open further possible actions of tizanidine exerted directly on spinal interneurons.

Simulation of motion on the skin. IV. Responses of Pacinian corpuscle afferents innervating the primate hand to stripe patterns on the OPTACON.

1. To measure spatial acuity of Pacinian corpuscle (PC) afferents in the median and ulnar nerves of macaque monkeys, we displayed horizontal bar patterns spaced 1-13 mm apart on a computer-controlled OPTACON stimulator contacting the hand. Two-point resolution was measured by simultaneously pulsing pairs of rows at rates of 100, 50, and 25 Hz; each pair was shifted in tandem across the skin in 1.2-mm steps to simulate tangential motion at speeds of 30-120 mm/s. Single-fiber responses are reported from eight physiologically identified PC afferents innervating the fingers and palm in anesthetized monkeys. 2. Pacinian afferents differ in their sensitivity to stripe patterns moved across the hand. Bursting PCs fire bursts of two or three spikes/pulse when one of the bars is close to the field center and one spike/pulse when adjacent bars straddle the center. These bursts result in double-peaked response profiles at stripe spacings greater than or equal to 2.4 mm. The passage of individual stripes over the field center is therefore represented by bursts of impulses superimposed on a continuous spike train. Unfortunately, many of these fibers also demonstrate fluctuations in firing that appear unrelated to the stripe pattern and therefore obscure its clear representation. 3. The remainder of the PC population displays uniform-sensitivity responses that resemble those previously reported for rapidly adapting (RA) afferents. They fire one spike/pulse as long as at least one of the bars is contained within the field. They merge individual stripes spaced less than one field diameter apart and show a pause in firing at wider spacing. Spatial resolution of gaps in the stripe pattern is therefore determined by receptive-field diameters, which extend up to 9.6 mm when tested with the OPTACON. 4. PCs display poorer spatial resolution than RAs, because of their larger receptive fields and less regular firing patterns. Only two of eight PCs tested demonstrated a pause in activity representing the gap between bars spaced 4.8 mm apart, whereas 11 of 14 RAs ceased firing briefly between stripes. Resolution of the individual stripes by all of the PCs tested was observed only at bar spacings of 1 cm (8 rows) or more. Spatial resolution of stripes is further impeded by the tendency of PC afferents to summate inputs from stripes spaced less than 2.4 mm apart; this results in response profiles with a single, large-amplitude broad peak.(ABSTRACT TRUNCATED AT 400 WORDS)

Simulation of motion on the skin. III. Mechanisms used by rapidly adapting cutaneous mechanoreceptors in the primate hand for spatiotemporal resolution and two-point discrimination.

1. The contribution of rapidly adapting (RA) mechanoreceptors to two-point discrimination has been evaluated by examining their ability to resolve the spacing of grating patterns shifted across the skin. The experiments test two different neural coding mechanisms that have been proposed to underlie resolution of spatial detail on the hand: 1) a rate-intensity code in which the spacing of surface features is encoded by the average frequency of firing of individual sensory afferents, and 2) an isomorphic representation of shape in which variations in the firing patterns of individual afferents reflect the spatiotemporal profile of skin indentation. 2. To measure the spatial acuity of RA mechanoreceptors innervating the hands of macaque monkeys, we displayed pairs of horizontal bars spaced 1-13 mm apart on a computer-controlled OPTACON stimulator placed over glabrous skin. Two-point resolution was measured by simultaneously pulsing pairs of rows at rates of 100, 50 and 25 Hz; each pair was shifted in tandem across the hand to simulate lateral motion. Single-fiber recordings were made from physiologically identified RA afferents in anesthetized monkeys. 3. Receptive field diameter appears to be the critical determinant of spatial resolution of gaps between two bars. RAs fire continuously if bar spacing is less than the field diameter but do not summate inputs when both active rows are contained within the field. Response profiles evoked by two bars spaced less than 4.8 mm apart can be predicted from the single-bar profiles, assuming occlusion between overlapping inputs with the strongest member dominating axonal output. Two-thirds of the RAs tested discharge 1 spike/pulse as bar patterns cross the field, yielding a uniform spike train whose frequency reflects stimulus pulse rates but fails to indicate gaps between bars. An additional 17% fire 2 spikes/pulse when the bars contact or straddle the field center, but also fail to differentiate individual stripes spaced less than 3.6 mm apart. 4. Only 17% of RAs represent gaps narrower than the field diameter. These fibers show double-peaked response profiles to bar patterns spaced at least 2.4 mm apart, firing 2 spikes/pulse as first one, and then the second stripe crosses the field center. Timing between peaks corresponds to bar spacing. Responses are reduced in amplitude when adjacent bars straddle the field center, as occlusion between simultaneous inputs prevents summation of inputs from the two stimuli. Fifteen of 16 RAs failed to resolve bars spaced 1.2 mm apart, as double-spike responses were evoked only by the leading stripe.(ABSTRACT TRUNCATED AT 400 WORDS)

Long term recordings in the cat motor cortex: unit activity and field potentials from sensory and brain stem stimulation as a means of identifying electrode position.

A method of chronically implanting microwires (25 microns diameter, 90% Pt/10% Ir wire) in the cat pericruciate cortex is described. These wires can obtain simultaneous recordings of single and multiunit activity from different sites and multiple recordings from the same site on different postoperative days. The electrodes were permanently implanted in the anaesthetized animal and left in place. Recordings were carried out in the awake, unrestrained cat. Different units were recorded as a result of spontaneous electrode movement in the cortex. Movement was documented with field potential recording from the implanted electrodes and resulted in changes in the latency and polarity of the initial components of the cutaneous field potential and changes in the number of components of the field potential elicited from brain stem stimulation. Changes in the receptive fields of the units, changes in the number of units antidromically invaded from brain stem stimulation, and in the threshold and occurrence of muscle activity elicited from intracortical microstimulation supported the evidence of electrode movement obtained from field potential recordings and could be used to document electrode movements tangential to the plane of the cortical laminae. Movement was a slow gradual process throughout the period of implantation. The longest period from which a single unit could be recorded was 2 days. The need for this neurophysiological analysis is supported by evidence for irregular electrode movement which could not have been reconstructed from histological examination of the cortex.

Simulation of motion on the skin. I. Receptive fields and temporal frequency coding by cutaneous mechanoreceptors of OPTACON pulses delivered to the hand.

1. Tactile discrimination of form requires motion of the hand across the object scanned. To dissociate lateral distortion of the skin from neuronal processing mechanisms involving multiple receptor classes and parallel central networks, we have simulated motion of bar patterns across the fingers and palm by the use of a computer-controlled grid of sequentially activated probes (OPTACON stimulator). Horizontal bar patterns have been swept across the hand at speeds of 30-120 mm/s to quantitatively characterize responses of cutaneous mechanoreceptive afferents recorded in the median and ulnar nerves. 2. Mechanoreceptors with phasic responses to pressure are activated by spatial patterns on the OPTACON, whereas those with tonic pressure responses are not; moving-bar patterns strongly excite both Meissner's afferents [rapidly adapting (RA) mechanoreceptors] and Pacinian corpuscles (PCs) but fail to excite slowly adapting (SA) afferents. OPTACON-type stimulators thus allow selective activation of phasic mechanoreceptor channels with spatially complex stimuli. 3. RA afferents respond in an all-or-none fashion to activation of two to five adjacent rows spanning 1-5 mm on the finger, with nearly identical latencies on all trials; response profiles are remarkable for their regularity and reproducibility. PCs have larger fields (4-13 rows) and stronger but more irregular responses than RAs. 4. Uniform sensitivity throughout the receptive field is a consistent feature of RA responses. Individual mechanoreceptor terminals appear to have equal access to the spike initiation zone and provide the same amplitude input as the fiber discharges 1 spike/pulse at each field location in 75% of the RAs tested. Uniform sensitivity allows each afferent to transmit a repetitive signal of the parameter of interest such as object speed, contour, or texture. 5. One-quarter of RAs fire two spikes to probe indentation and retraction at the field center. Such graded responses are usually observed in only one direction of motion, reflecting a preferred sequence of receptor activation rather than a specific location on the skin. PCs fire bursts of two to four spikes throughout most of their receptive fields; sensitivity is broadly distributed rather than peaked. Thus phasic mechanoreceptors fail to provide a precise signal of stimulus location; localization at the level of individual papillary ridges appears to be signaled by a population mechanism involving unique combinations of RA, SA, and PC afferents.(ABSTRACT TRUNCATED AT 250 WORDS)

Simulation of motion on the skin. II. Cutaneous mechanoreceptor coding of the width and texture of bar patterns displaced across the OPTACON.

1. These experiments assay the functional significance of receptive-field architecture for information processing. Rapidly adapting (RA) afferents have been previously shown to converge information from clusters of 14-25 Meissner's corpuscles, whereas afferents innervating Pacinian corpuscles (PCs) have only a single, large receptor terminal. We tested two opposing hypotheses of functional architecture: 1) summation models, in which an afferent integrates signals from all of its terminals, showing monotonic increases in activity as a function of contact area, and 2) winner-take-all models, in which the most strongly activated receptor in the cluster dominates axonal output by cancellation of signals from other branches. 2. Bar and stripe patterns have been swept across the finger or palm of the monkey's hand at speeds of 30-120 mm/s with the use of a computer-controlled grid of sequentially activated miniature probes (OPTACON stimulator). The dense packing of OPTACON probes permits placement of up to five groups of stimulators within an individual receptive field, allowing us to activate one or more clusters of Meissner's corpuscles simultaneously and to stimulate the bulbar corpuscle of PC afferents at different orientations through the skin. Integration of information from moving bar patterns has been tested with two protocols. In the variable width protocol, the total number of activated rows in the pattern is varied from one to five, with a constant spacing of 1.2 mm between pulsed rows. In the variable density protocol, the length of skin stimulated is held constant at 5 mm and the spacing of stimuli varied. 3. RA afferents show no evidence of summation of inputs within their receptive fields. Motion of wide bars across the field increases the duration of firing but not the total spikes evoked by each pulse. Responses to the leading edge of wide bars were found to be identical to those evoked by a single-row bar. Simultaneous activation of two to five rows evokes the same or fewer spikes per pulse than the most effective individual row tested alone. When broad-bar patterns are centered over the field, contacting the maximum number of receptors, RAs follow activity in the dominant branch or terminus, suppressing additional inputs. Lack of summation is observed at all pulse frequencies tested (25-100 Hz). 4. Moving bar patterns evoke responses as long as at least one row stimulates the receptive field; broader patterns evoke longer spike trains whose total number of impulses is proportional to bar width.(ABSTRACT TRUNCATED AT 400 WORDS)

The responses of pericruciate cortical neurones to distal forepaw electrical stimulation in the unanaesthetized, unrestrained cat.

Experiments were performed to examine the responses of cortical neurons in the pericruciate cortex to cutaneous afferent input from the distal forepaw. Ninety-nine cortical neurons responding to electrical stimulation of the forepaw were recorded from four cats. Their response latencies ranged from 6 to 23 ms. The units had cutaneous receptive fields which ranged in size from those restricted to one digit to those extending over the whole forelimb. They were recorded from area 4 and area 3. Intracortical microstimulation at the recording sites activated either the distal or proximal musculature of the forelimb. When the characteristics obtained from each recording site were examined as a group of features, a uniform population emerged which was significantly different from the rest of the sample. These units had the shortest latency responses to distal forepaw electrical stimulation, the shortest duration of evoked discharge, the smallest distal cutaneous receptive fields. Such units were recorded at the border between areas 3 and 4, at sites which on microstimulation resulted in movements of the distal forepaw musculature.

The responses of cat motor cortical units to electrical cutaneous stimulation during locomotion and during lifting, falling and landing.

Experiments were performed to examine the influence of cutaneous information on motor cortical cells during movement in intact, awake cats. The movements investigated were locomotion and a sequence in which the animal was repeatedly lifted and dropped. Electrical stimuli to distal skin areas were delivered periodically during the movements and responses of motor cortical cells were examined. The animals used in these experiments were chronically implanted with cortical microelectrodes, a pyramidal tract stimulating electrode, cutaneous stimulating electrodes in the forepaw, and a recording cuff electrode around the median nerve. EMG electrodes were implanted in several forelimb muscles and a length gauge was implanted across the elbow joint. Results included in this report were obtained from three cats. The twenty-two cortical units analysed in this study (seven were PT units) were selected from a larger sample by the following criteria: cutaneous receptive fields which included the distal part of the limb, consistent short latency responses to electrical cutaneous stimulation and spontaneous activity modulated in consistent patterns during the movement investigated. Sixteen units were recorded during locomotion, 12 during the lifting and dropping cycle and 6 of these during both conditions. Most of the cells were influenced by the cutaneous input during locomotion. Three units had no response to peripheral stimulation during locomotion though they were responsive to this stimulus when the animal was sitting quietly. All the cells were responsive to the cutaneous input during the lifting and dropping cycle. The responses to cutaneous stimuli were found to be modulated in relation to phases of the step cycle and the lifting and dropping cycle. In 13 units this modulation did not parallel the modulation of the unit's spontaneous firing during these activities. For these units a common finding during locomotion was that the response to cutaneous stimuli increased throughout stance, reached maximum during the flexion part of the swing, and then declined to a minimum during the beginning of the next stance. During the lifting and dropping cycle, the responses were greatest when the animal was held in the air and when starting to fall, and minimal just prior to and after landing. In both movements, cutaneous responses were reduced when the limb was used to support the animal's weight. There is apparently a movement phase-related modulation of cutaneous input to some motor cortical cells. This modulation of cutaneous input resembled the modulation of cutaneous reflexes during locomotion.(ABSTRACT TRUNCATED AT 400 WORDS)