John A. Hanson

Postural set and overt movement: a force-platform analysis.

If the postural set is altered by changing the habitual balance of the head during a movement performed against gravity, the subjective feeling of weight can be markedly reduced. For the movement from sitting-to-standing an objective record of force distribution corresponding to the differences in feeling tone reported by S has been obtained with a strain-gauge force platform. The force platform appears well adapted for studying the relation between postural set and overt movement.

Heart Rate and Small Postural Changes in Man

Heart rates of eleven normal male subjects were recorded in a number of different sitting and standing postures. Three of the sitting postures were recorded both with and without an attention-demanding task. Heart rates differed significantly among many of the postures but not between task conditions.

Fatigue Effects on Patterns of Movement

The standing broad jump and four other gross body movements were analysed by colour-coded multiple-image photography before and after three kinds of fatigue-inducing exercise. For each movement marked individual differences in style of performance were found which tended to persist despite the effects of fatigue. Certain linear and angular measures taken from the movement patterns proved to be sensitive to fatigue effects. The amount and significance of change in the different indices varied with the method used for inducing fatigue.

Studies on Dark Adaptation. VII. Effect of Pre-Exposure Color on Foveal Dark Adaptation*

The effect of pre-exposure color on foveal dark adaptation was investigated. Monocular absolute threshold curves were obtained for two observers with white, red, green, and blue test patches after white, red, green, and blue pre-exposures. All combinations of pre-exposure and test-patch color were measured for each of two sizes of centrally fixated test patch: 48 min; and 2 deg 16 min. The pre-exposure field was centrally fixated and subtended 10 deg. The pre-exposure luminance and duration was 100 ft-L for 100 sec prior to threshold determinations with the smaller test patch, and 10 ft-L for 10 sec prior to threshold determinations with the larger test patch. The duration of the test flash was 0.033 sec. The results indicated the absence of pre-exposure color effects in the rod-free fovea, with the exception that pre-exposure to red light reduced subsequent sensitivity to the long-wavelength part of the spectrum to a slightly greater degree than did pre-exposure to any of the other colors tested. The results for the larger rod-populated foveal area demonstrated effects consistent with the scotopic luminance of the pre-exposure colors which were used.

Studies on Dark Adaptation. V. Effect of Various Sizes of Centrally Fixated Pre-Exposure Fields on Foveal and Peripheral Dark Adaptation*

The effect of various sizes of centrally fixated pre-exposures on foveal and peripheral dark adaptation was investigated. For both foveal and peripheral determinations, absolute brightness sensitivity was measured monocularly with a 1-deg circular test patch. Peripheral locations tested were 2, 6, and 15 deg on the horizontal meridian of the temporal retina. Foveal dark-adaptation curves were obtained after pre-exposure to fields which subtended 1, 2.5, 5, 10, and 37.5 deg diam. Peripheral dark-adaptation curves were obtained for three sizes of pre-exposure field at each location. In the fovea, each size was presented at 1 ft-L for 10 sec, 100 ft-L for 10 sec, and 1000 ft-L for 100 sec. In the periphery, each size was presented at 0.1 ft-L for 10 sec and 10 ft-L for 10 sec. The foveal results, with one exception, indicated that size is not a differential factor. In the periphery, the effects of size were most pronounced between those sizes which did and those which did not stimulate the area tested.

Studies on Dark Adaptation. VI. Effects on Foveal Dark Adaptation of Series of Alternating Light and Dark Periods

This study investigated the effects on foveal dark adaptation of series of alternating light and dark periods. The purpose of the study was to determine the duration of dark period necessary to avoid the cumulative effects of successive light periods on foveal adaptation. Absolute brightness thresholds were measured monocularly. The test patch which subtended 1 deg diam, and the pre-exposure which subtended 37.5 deg diam were centrally fixated. Foveal dark-adaptation curves were obtained after 10 and 25 presentations of each of the following light and dark period combinations: (1) 1 ft-L for 10 sec with dark periods of 0, 10, and 25 sec, (2) 10 ft-L for 1 sec with dark periods of 0 and 10 sec, (3) 0.1 ft-L for 10 sec with dark periods of 0, 10, and 25 sec, (4) 1 ft-L for 1 sec with dark periods of 0 and 10 sec, and (5) 0.1 ft-L for 1 sec with dark periods of 0 and 10 sec. Curves were also obtained after single presentations of each light period. In most cases, the longest dark period duration tested appeared to minimize or cancel any cumulative effects of the repeated presentations.

Studies on dark adaptation. IV. Pre-exposure tolerance of the dark-adapted peripheral retina.

The effects of low-brightness short-duration pre-exposures on peripheral dark adaptation were investigated. Three peripheral locations: 2 deg, 6 deg, and 18 deg, were tested with a square 1-deg test patch of 0.033 sec duration. Pre-exposure was to a centrally fixated circular field which subtended 55-deg diam. Monocular curves were obtained after pre-exposures of 0.01, 0.1, 1, and 10 ft-L each presented for 1 and 10 sec. All pre-exposure conditions resulted in some loss of sensitivity at the 2-deg location; pre-exposure combinations of 0.01 and 0.1 ft-L-sec resulted in little if any loss of sensitivity at the 6-deg and 18-deg locations.