Biomedical subjects

J W Morley

Publications and source records attributed to J W Morley.

26 records · Page 2Linked to original sources

PubMed1991

A method for the generation of complex vibrotactile stimuli.

A method is described utilizing computer-generated sine wave data and purpose-built hardware to generate a complex vibrotactile stimulus. Two sine waves of different frequency were summed to produce a complex waveform with two temporal components, a high frequency component and a low frequency beat component. The computer-generated data points for each of the two component sine waves were downloaded to two banks of static memory in a dual synchronous arbitrary function generator. The data points in memory were fed to two 12-bit digital-to-analogue converters which sent the two analogue sine wave signals to a summing amplifier where the two sine waves were added. This method provides a complex waveform that can be gated on and off, has a fixed frequency ratio of the component sine waves and no phase drift between the component waves. Addition of the separate sine waves in a summing amplifier allows for easy alteration of the amplitude ratio of the sine waves. The output of the summing amplifier is sent to a feedback controlled mechanical stimulator, thereby allowing the stimulus to be presented to the skin of human subjects and experimental animals.

Computers↗

PubMed1990

Perceived pitch of vibrotactile stimuli: effects of vibration amplitude, and implications for vibration frequency coding.

1. The effect of changes in amplitude on the perceived pitch of cutaneous vibratory stimuli was studied in psychophysical experiments designed to test whether the coding of information about the frequency of the vibration might be based on the ratio of recruitment of the PC (Pacinian corpuscle-associated) and RA (rapidly adapting) classes of tactile sensory fibres. The study was based on previous data which show that at certain vibration frequencies (e.g. 150 Hz) the ratio of recruitment of the PC and RA classes should vary as a function of vibration amplitude. 2. Sinusoidal vibration at either 30 Hz or 150 Hz, and at an amplitude 10 dB above subjective detection thresholds was delivered in a 1 s train to the distal phalangeal pad of the index finger in eight human subjects. This standard vibration was followed after 0.5 s by a 1 s comparison train of vibration which (unknown to the subject) was at the same frequency as the standard but at a range of amplitudes from 2 to 50 dB above the detection threshold. A two-alternative forced-choice procedure was used in which the subject had to indicate whether the comparison stimulus was higher or lower in pitch (frequency) than the standard. 3. Marked differences were seen from subject to subject in the effect of amplitude on perceived pitch at both 30 Hz and 150 Hz. At 150 Hz, five out of the eight subjects reported an increase in pitch as the amplitude of the comparison vibration increased, one experienced no change, and only two experienced the fall in perceived pitch that is predicted if the proposed ratio code contributes to vibrotactile pitch judgements. At 30 Hz similar intersubject variability was seen in the pitch-amplitude functions. 4. The results do not support the hypothesis that a ratio code contributes to vibrotactile pitch perception. We conclude that temporal patterning of impulse activity remains the major candidate code for pitch perception, at least over a substantial part of the vibrotactile frequency bandwidth.

Female↗

PubMed1988

Vibratory detection thresholds following a digital nerve lesion.

Vibratory detection thresholds were measured at a number of frequencies between 5 and 320 Hz following a lesion of the lateral digital nerve innervating the terminal phalanx of the left index finger. Thresholds measurements began approximately 4 weeks after the nerve was repaired. A staircase method was used to determine thresholds on both the injured fingerpad and the intact fingerpad of the opposite hand. There was a large increase in thresholds on the injured fingerpad in the lower range of frequencies (5-40 Hz) while at higher frequencies (80-250 Hz) there was no significant difference between the thresholds on the injured fingerpad and those on the intact fingerpad. It is suggested that the differential effect of the nerve lesion on vibratory thresholds reflects the spread of the vibratory stimulus through the skin and the spatial characteristics of functionally intact receptor/afferent groups innervating neighbouring skin.

Fingers↗

PubMed1987

Sinusoidal movement of a grating across the monkey's fingerpad: representation of grating and movement features in afferent fiber responses.

Gratings of alternating grooves and ridges were moved sinusoidally back and forth across the monkey's fingerpad. Each grating was completely specified by its spatial period and the movement by its peak speed: together these determined the peak temporal frequency at which grating ridges passed over the skin. Responses of cutaneous, mechanoreceptive afferents innervating the fingerpad were characterized in terms of these 3 parameters. Slowly adapting afferents (SAs), rapidly adapting afferents (RAs), and Pacinian afferents (PCs) had different characteristics. The responses (mean cyclic discharge rates) of the SAs increased when the spatial period of the grating increased (and peak speed of movement remained constant) but did not change with changes in the peak speed of the movement (while the spatial period of the grating remained constant). Conversely, the responses of the PCs increased when the peak speed of movement increased (and the spatial period remained constant) but were relatively insensitive to changes in the spatial period of the grating (while the peak speed remained constant). The responses of the RAs increased as the spatial period of the grating increased (and peak speed remained constant) and also increased as the peak speed of movement increased (and the grating spatial period remained constant). When the peak temporal frequency of the grating ridges was held constant, the responses of all 3 afferent groups changed with changes in the grating spatial period or in the peak speed of movement. Information about the spatial features of the grating, independent of the peak speed of movement, was present in the SA population response and in the ratios of the RA and PC population responses. Information about the peak speed of movement, independent of the spatial period of the grating, was present in the PC population response and could be extracted from the RA population response.

Action Potentials↗

PubMed1987

Sinusoidal movement of a grating across the monkey's fingerpad: temporal patterns of afferent fiber responses.

Responses were recorded from cutaneous afferents innervating mechanoreceptors in the monkey's fingerpad, while gratings of alternating grooves and ridges were moved sinusoidally across their receptive fields. The gratings were specified by their spatial period and the movement by its peak speed: together these determined the peak temporal frequency at which grating ridges passed over the receptive field. During the central 42 degrees of each half cycle of movement, the speed and thus the temporal frequency of the grating ridges remained constant to within 6.6% of their peak values. In this region the responses of all afferents were phase-locked to the temporal sequence of grating ridges. The number of impulses elicited by each grating ridge was a function of the stimulus variables. For all 3 afferent classes--namely, slowly adapting afferents (SAs), rapidly adapting afferents (RAs), and Pacinian afferents (PCs)--the number of impulses per grating ridge increased as the spatial period of the grating increased (while the peak speed of movement was held constant). Similarly, for all 3 classes, the number of impulses per ridge decreased as the peak speed of movement increased (while the spatial period of the grating remained constant). When the peak temporal frequency of the grating ridges was held constant, for SAs and RAs the number of impulses per ridge increased with an increase in the spatial period of the grating and thus with an increase in the peak speed. These phase-locked responses provided information about the peak temporal frequency of the grating ridges independent of the grating spatial period and of the peak speed of movement. The shape of the response profile during a half cycle of movement was different for different afferents. Many of the RA response profiles were close to sinusoidal. The SA and PC profiles tended to have reduced peaks or raised troughs, resulting in flatter profiles. Other departures from sinusoidal profiles were also seen.

Action Potentials↗

PubMed1987

Sinusoidal movement of a grating across the monkey's fingerpad: effect of contact angle and force of the grating on afferent fiber responses.

Responses were recorded from cutaneous afferents innervating mechanoreceptors in the monkey's fingerpad. When gratings of alternating grooves and ridges were moved sinusoidally back and forth across the receptive field, the responses of the afferent were often not equal for the 2 directions of movement. To investigate this phenomenon, the position of the center of the afferent's receptive field, relative to the contact area between the grating and the finger, was varied systematically. For some afferents, regardless of these relative positions, the response was always greater for a particular direction of movement. For other afferents, regardless of these relative positions, the responses for the 2 directions of movement were always equal. For a minority of afferents, the response was greater for movement in one particular direction for some relative positions and greater for movement in the opposite direction for other relative positions. Slowly adapting afferents (SAs), rapidly adapting afferents (RAs), and Pacinian afferents (PCs) exhibited all 3 types of response patterns. We could not relate these patterns to the afferent type or to the positions, in the fingerpad, of the receptive field center. The contact force between the grating and the finger was varied by varying the contact displacement (indentation). Two grating spatial periods were used. For SAs and PCs the response increased with increasing indentation for both gratings. For RAs the response to the finer grating increased with increasing indentation, but the response to the coarser grating did not.

Action Potentials↗

PubMed1985

A stimulator for moving textured surfaces sinusoidally across the skin.

The stimulator allows textured surfaces to be moved sinusoidally across the skin of the fingerpad. Sinusoidal motion is produced by a "scotch yolk" driven by a DC motor. The amplitude of movement is adjustable up to a maximum of 80 mm peak to peak and the frequency is continuously adjustable from 0.1 Hz to 2.0 Hz. Movement of the surface is monitored by an optical transducer and contact force between the finger and the surface is monitored by a strain gauge bridge. The stimulator is simple and robust and is suitable for both neurophysiological and psychophysical experiments in animals and humans.

Animals↗

PubMed1983

Tactile discrimination of gratings.

Human subjects were required to differentiate grating surfaces of alternating grooves and ridges by moving a finger back and forth across the surface. Their discriminative capacities were measured, as well as the movement and force profiles that they selected. To measure discrimination, a forced choice paradigm was used in which three surfaces were presented on each trial. Two surfaces were the same (standards) and the subject was required to indicate which of the three surfaces (the comparison) differed from the other two. Two series of surfaces were used with standards whose spatial periods were 770 and 1002 mu, respectively. Subjects were able to discriminate, at the 75% correct level, two gratings which differed in spatial period by the order of 5%. When tangential movement between the surface and the finger was eliminated, and only radial contact permitted, discrimination was degraded and the 75% correct levels increased to the order of 10%. Subjects were free to choose their own patterns of finger movement and of contact force between finger and surface. Movement was measured cinematographically. For all subjects movement patterns were close to sinusoidal, with frequencies in the range of 4.0 Hz and with mean velocities of the order of 160 mm/s. Patterns of contact force were measured by a force transducer. For all subjects the force varied rhythmically in synchrony with movement, but the patterns and magnitudes varied with the subject. Gratings were scaled for perceived roughness by a magnitude estimation technique: the relationship between perceived roughness and grating period was monotonic.

Adolescent↗