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Biomedical subjects

G F Miller

Publications and source records attributed to G F Miller.

29 records · Page 2Linked to original sources
PubMed1993

Transformations between visual and kinesthetic coordinate systems in reaches to remembered object locations and orientations.

The abilities of human subjects to perform reach and grasp movements to remembered locations/orientations of a cylindrical object were studied under four conditions: (1) visual presentation of the object-reach with vision allowed; (2) visual presentation-reach while blindfolded; (3) kinesthetic presentation of the object-reach while blindfolded and (4) kinesthetic presentation-reach with vision. The results showed that subjects were very accurate in locating the object in the purely kinesthetic condition and that directional errors were low in all four conditions; but, predictable errors in reach distance occurred in conditions 1,2, and 4. The pattern of these distance errors was similar to that identified in previous research using a pointing task to a small target (i.e., overshoots of close targets, undershoots of far targets). The observation that the pattern of distance errors in condition 4 was similar to that of conditions 1 and 2 suggests that subjects transform kinesthetically defined hand locations into a visual coordinate system when vision is available during upper limb motion to a remembered kinesthetic target. The differences in orientation of the upper limb between target and reach positions in condition 3 were similar in magnitude to the errors associated with kinesthetic perceptions of arm and hand orientations in three-dimensional space reported in previous studies. However, fingertip location was specified with greater accuracy than the orientation of upper limb segments. This was apparently accomplished by compensation of variations in shoulder (arm) angles with oppositely directed variations in elbow joint angles. Subjects were also able to transform visually perceived object orientation into an appropriate hand orientation for grasp, as indicated by the relation between hand roll angle and object orientation (elevation angle). The implications of these results for control of upper limb motion to external targets are discussed.

Adolescent↗
PubMed1993

An objective criterion for apparent motion based on phase discrimination.

Studies of visual apparent motion have relied on observers' subjective self-reports of experienced motion, for which there is no objective criterion of right or wrong. A new method of phase discrimination is reported that may offer an objective indicator of apparent motion. Ss discriminated the direction of an objective 75-ms phase shift, away from strict temporal alternation of 2 stimulus dots. Accuracy increased from 50% to 100% correct as rate of alternation and distance between the dots was decreased, in conformity with Korte's third law of apparent motion. This and additional evidence suggests that phase discrimination may be mediated by asymmetries between the experienced strengths of leftward and rightward motion. Phase discrimination may also be adaptable to the study of apparent motion and related phenomena in other sensory modalities and other animal species.

Adult↗
PubMed1992

Further evidence against a direct automatic neuromotor link between the ACL and hamstrings.

The purpose of this experiment was to determine whether reflexive, or more broadly, automatic hamstrings excitation could be elicited during isometric, maximum effort, step increases in knee extension torque. Eight healthy subjects without lower extremity dysfunction or injury performed maximum effort isometric knee extension at 15 and 85 degrees of knee flexion in minimum elapsed time. Surface electromyography was used to record medial (semimembranosis and semitendinosis) and lateral (biceps femoris--long head) hamstrings excitation that was subsequently normalized to the excitation during maximum isometric knee flexion. To assess whether automatic hamstrings excitation was elicited, the amplitude of the EMG signals was analyzed and compared for 50 ms prior to peak knee extension torque, and three consecutive 50 ms windows following peak knee extension torque. The amplitude of the EMG subsequent to the peak knee extension torque failed to support the contention of an automatic hamstrings excitation mediated by neural circuitry from the ACL. The present results, in conjunction with previous work, suggest that a protective automatic hamstrings contraction is not normally elicited in response to conditions subjecting the anterior cruciate ligament to strain.

Adult↗
PubMed1991

Fatigue rates of vastus medialis oblique and vastus lateralis during static and dynamic knee extension.

Fatigue rates of the vastus medialis oblique and vastus lateralis muscles were compared from static and dynamic exercise. Based upon clinical observations, it was expected that the vastus medialis oblique would demonstrate greater fatigability than the vastus lateralis. However, based upon physiological and morphological considerations, it was expected that the vastus lateralis would exhibit greater fatigability than the vastus medialis oblique. In the static exercise condition, nine subjects--having no history of knee problems--maintained an isometric knee extension torque at 30 and 60% of their maximum value until exhaustion, during which time electromyography (EMG) data were collected every 10 s. The knee angle was 20 degrees flexion. In the dynamic exercise condition, a different group of seven subjects performed exercise sets consisting of eight cycles of concentric-eccentric knee extension, with a resistance equal to 40% of the maximum isometric value. The range of motion was restricted to the terminal 30 degrees of knee extension. Each set of eight repetitions was followed by a 1 s 50% maximum isometric knee extension, during which time EMG data were collected. The raw EMG data were numerically processed to extract the median frequency of the power density spectrum, which has been shown to reflect the metabolic processes associated with fatigue. Linear regression generated a slope coefficient representing the rate of change of the median frequency, with respect to contraction duration for each subject, muscle, and condition. Analyses of variance, with repeated measures from both exercise conditions suggest that "short-arc" quadriceps exercise did not selectively fatigue either the vastus medialis oblique or vastus lateralis, thereby supporting neither clinical nor physiological expected outcomes. Therefore, the clinical contention that short-arc quadriceps exercises selectively strengthen the vastus medialis oblique is questioned.

Adult↗