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Biomedical subjects

A W Goodwin

Publications and source records attributed to A W Goodwin.

At least 37 records · Page 2Linked to original sources
PubMed1989

Tactile discrimination of thickness.

The ability of human subjects to discriminate plane metal plates of different thickness was measured using of forced-choice paradigm. The plates, made by electroplating a thin layer of copper onto flat brass shims, were gripped between the thumb and the index finger. Subjects were presented with either 2 standard plates (0.2 mm thick), or a standard plate and a test plate that was slightly thicker, and were required in state which alternative had occurred. When the edges of the plates could not be touched, a difference in thickness of about 0.075 mm could be discriminated. Surprisingly, when the edges were included in the grip, performance did not improve. All hypotheses of strategies used by the subjects required them to sense the angles of the finger joints with a precision of about 0.1 degrees.

Adult↗
PubMed1989

Skin profiles during sinusoidal vibration of the fingerpad.

Skin on the fingertips of humans and monkeys was stimulated by a probe vibrating with a sinusoidal displacement. The probe and the skin were illuminated stroboscopically and were viewed through a dissecting microscope. The stroboscope was triggered by the sinusoidal generator via a digital delay, so that the position of both the probe and the skin could be measured at regular intervals during the cycle. Six frequencies and 3 amplitudes of vibration were used. During a portion of the cycle the probe and the skin separated, so that the skin waveform was a clipped sinusoid. An increase in stimulus frequency increased the fraction of the cycle during which the probe and the skin were separated. Adding a static pre-indentation to the vibration reduced this fraction, and for this condition a decrease in vibratory amplitude also decreased the fraction. Thus the skin motion contained harmonics that were not present in the probe motion, and the harmonic content differed for different stimulus conditions.

Animals↗
PubMed1989

Spatial and temporal factors determining afferent fiber responses to a grating moving sinusoidally over the monkey's fingerpad.

Gratings of alternating grooves and ridges were moved sinusoidally across the fingerpads of anesthetized monkeys, while responses were recorded from individual slowly adapting afferents (SAs), rapidly adapting afferents (RAs), and Pacinian afferents (PCs) in the median nerve. The stimulus comprised 2 spatial variables, namely, groove width (G) and ridge width (W), and 2 temporal variables, namely, the peak speed of movement (S) and the peak temporal frequency (F) at which successive spatial cycles of the grating pass over a point in the receptive field. The responses of all 3 fiber types were determined by only 1 spatial variable, G, and only 1 temporal variable, F. Changes in W or S affected responses only if there was a concomitant change in either G or F. Responses were phase-locked to the occurrence of successive spatial cycles of the grating, and we have used the number of impulses elicited by a single spatial cycle as the fundamental measure of response. An equation of the form I = cGaexp(-b square root of F) describes the responses of all 3 fiber types. For SAs, the effect of groove width was greater (a = 2.64) than for RAs and PCs (a = 0.924 and 1.05, respectively). The reduction in response with frequency was most marked for SAs (b = 0.262), and greater for PCs (b = 0.167) than for RAs (b = 0.130). From the equation, the instantaneous response during the entire sinusoidal cycle was reconstructed as well as a second measure, the mean cyclic response. These 2 measures behaved differently with changes in the stimulus parameters. The temporal properties of the fibers, as revealed by gratings, may appear to be in conflict with those established by vibratory threshold studies; in fact, they are compatible with suprathreshold responses to vibrating probes.

Animals↗
PubMed1989

Perceived roughness of a grating: correlation with responses of mechanoreceptive afferents innervating the monkey's fingerpad.

Human subjects scaled gratings of alternating grooves and ridges for perceived roughness. Roughness increased with an increase in groove width and decreased with an increase in ridge width, but the effect of groove width was much greater than the effect of ridge width. In corresponding neurophysiological experiments, the gratings were moved sinusoidally across the receptive fields of single mechano-receptive afferents innervating the fingerpads of anesthetized monkeys. The measure of response used was the mean cyclic discharge rate (averaged over one cycle of the sinusoid). Slowly adapting afferents (SAs), rapidly adapting afferents (RAs), and Pacinian afferents (PCs) all showed a marked increase in response when groove width increased. An increase in ridge width had no consistent effect on the responses of SAs or RAs but resulted in a small decrease in the response of PCs. The response to a smooth surface differed significantly from the responses to the finer gratings only for the RAs. An alternative measure of response (the number of impulses elicited by each spatial cycle of the grating) increased with an increase in ridge width for all 3 fiber types. Thus, the large effect of groove width on perceived roughness can be accounted for by the mean cyclic discharge rate in the active afferent fibers. The smaller effect of ridge width can be accounted for by the number of impulses per spatial cycle of the grating.

Adult↗
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↗
PubMed1978

Spatial summation of responses in receptive fields of single cells in cat striate cortex.

Spatial summation of responses in striate neurons in cats under N2O/O2 anaesthesia was examined quantitatively both along the line of the optimal stimulus orientation (length summation) using moving light bars and single light and dark edge stimuli, and at right angles to the optimal orientation (width summation) using stationary flashing bars. Activity profiles and length-response curves were prepared from simple, complex and hypercomplex I and II cells. An activity profile indicates the responsiveness of a cell at locations along the length of its receptive field. The activity profiles from all cell types were usually well fitted by Gaussian functions. Length summation occurs both in end-free (simple and complex) and, to a lesser extent, in end-stopped (hypercomplex I and II) cells over a wide range of stimulus contrasts (0.13 to 0.95). The linearity of length summation was tested either by comparing the recorded length-response curves with the curves predicted from the linear integration of the activity profiles or by comparing the response to the activation of two regions of the receptive field with the sum of the responses to each region activated separately. Although length summation was usually non-linear (either greater than or less than direct proportionality) it was more nearly linear in complex than it was in simple and hypercomplex I cells. Mechanisms responsible for non-linear length summation were studied, including a threshold for discharge, response saturation and summation of end-zone inhibition. Complex cells show little width summation for bars wider than 0.3 degrees. In simple and hypercomplex I cells there was also relatively little width summation either in an ON or an OFF discharge region at contrasts above about 0.4 but at lower contrasts width summation may be apporximately linear. Spatial summation of responses does not appear to be a useful characteristic for distinguishing one striate cell type from another.

Animals↗
PubMed1978

The influence of stimulus velocity on the responses of single neurones in the striate cortex.

1. Using a multi-histogram technique forty-seven response-velocity curves were prepared for a variety of visual stimuli presented to twenty-one cells in the striate cortex of the anaesthetized, paralysed cat. 2. The character of each velocity-response curve varied according to the measurement used in assessing a response. Reasons are advanced for sampling the response over a single bin of short duration at the peak of the discharge in each average response histogram. 3. The sharpness of tuning varied markedly throughout the population of cells but it was not possible to establish any definitive class differences. 4. For simple and complex cell categories there was considerable overlap in both the range of effective stimulus velocities and the distribution of the optimal velocities. An observation not emphasized in the past was that some simple cells responded to very fast stimuli while a number of complex cells were driven by very slowly moving stimuli. 5. Generally changes in stimulus parameters such as the polarity of contrast of a moving edge, its orientation or direction of movement produced only slight modifications in the profile of the velocity-response curve. 6. The abolition of the response of simple cells that failed to be driven by rapidly moving stimuli was shown to be due to the entry of the stimulus into the inhibitory flank distal to the discharge region. When the movement of the stimulus was confined to the discharge region there was little evidence of velocity dependence in the response. The duration over which the inhibition from the distal flank remained effective was evaluated for representative simple cells.

Action Potentials↗
PubMed1977

Infradiaphragmatic total anomalous pulmonary venous connection to portal vein. Diagnostic implications of echocardiography.

A case of total anomalous pulmonary venous connection to the portal vein is described. The diagnosis was suspected clinically, supported by the echocardiogram, and confirmed by cardiac catheterisation, angiocardiography, and contrast echocardiography. An echo-free space lying behind the left atrium initially was thought to represent the common pulmonary vein. However, contrast echocardiography showed that this space was not the anomalous vein but probably an artefact. This paper shows that the origins of intracardiac echoes cannot always be assumed from a simple comparison of echocardiography with angiocardiographic or necropsy findings. In some cases it is necessary to introduce a marker into the echocardiogram which unequivocally originates from, and, therefore, localises, the structure under examination. Contrast echocardiography provides such a marker.

Angiocardiography↗
PubMed1975

Direction selectivity of simple striate cells: properties and mechanism.

Most simple cells in the striate cortex of the cat are direction selective, firing to broadside movement of an optimally oriented edge or bar in one direction of motion and not the other. The smallest stimulus displacement for which a direction-selective discrimination can be made cannot be smaller than the threshold for the detection of the displacement itself. It is shown that retinal image quality is an important limiting factor in respect to the thresholds both for stimulus displacement and direction selectivity.

Animals↗
PubMed1975

Direction selectivity of complex cells in a comparison with simple cells.

Following our earlier study on direction selectivity in simple cells (5), the present findings on complex cells made it possible to compare the direction selectivity in the two types of striate cell. Common properties were found in the dimension of the smallest stimulus displacement giving a direction-selective response and in the role of inhibition in suppressing the response as the stimulus moved in the nonpreferred direction. However, the effectiveness of this inhibition varied in the two cell types since it suppressed both driven and spontaneous activity in the simple cell, but only driven firing in the complex cell. It is argued that direction selectivity must enter the response before the complex cell if the inhibition responsible for it's generation fails to influence the spontaneous activity of the cell. The consequences of this finding are considered in the terms of parallel or sequential processing of visual information in striate cortex.

Animals↗