Biomedical subjects

X D Pang

Publications and source records attributed to X D Pang.

3 recordsLinked to original sources

PubMed1991

Visual evoked potential responses of the anesthetized cat to contrast modulation of grating patterns.

Contrast modulation affords independent control of static contrast (C) and changes in contrast (delta C). We found that in anesthetized, paralyzed cats, the visual evoked potential (VEP) was dependent only on magnitude of delta C at each pattern transition, and was independent of the starting or ending contrast level. Increasing modulation frequency to above 2 Hz reduced the VEP monotonically, implying that the time constant for differentiation by the VEP is of the order of 250 msec. The essentially perfect a.c. coupling suppresses standing contrast completely, permitting the full dynamic range of the VEP response system to be used for detection of contrast increments (which results in a decreasing Weber fraction). The difference between our results and those of behavioral studies using contrast modulation can be explained by eye movements present in the behavioral studies which refresh the retinal image of the static contrast in a way uncorrelated to temporal modulation of the stimulus, thus introducing a masking effect.

Anesthesia, General↗

PubMed1991

Manual discrimination of force using active finger motion.

In these experiments, two plates were grasped between the thumb and forefinger and squeezed together along a linear track. An electromechanical system presented a constant resistance force during the squeeze up to a predetermined location on the track, whereupon the force effectively went to infinity (simulating a wall) or to zero (simulating a cliff). The task of the subject was to discriminate between two alternative levels of the constant resistance force (a reference level and a reference-plus-increment level). Results of these experiments indicate a just noticeable difference of roughly 7% of the reference force using a one-interval paradigm with trial-by-trial feedback over the ranges 2.5 less than or equal to F0 less than or equal to 10.0 newtons, 5 less than or equal to D less than or equal to 30 mm, 45 less than or equal to S less than or equal to 125 mm, and 25 less than or equal to V less than or equal to 160 mm/sec, where F0 is the reference force, D is the distance squeezed, S is the initial fingerspan, and V is the mean velocity of the squeeze. These results, based on tests with 5 subjects, are consistent with a wide range of previous results, some of which are associated with other body surfaces and muscle systems and many of which were obtained with different psychophysical methods.

Biomechanical Phenomena↗

PubMed1986

Interaural magnification.

In principle, magnification of interaural differences, as could be achieved by the use of an enlarged head, will improve auditory spatial perception. This note presents some preliminary thoughts and observations on a signal-processing scheme for interaural magnification.

Auditory Perception↗