Recent investigators reported large adaptational effects in human vision dependent on the plane of linearly polarized light. In the present study, such adaptational effects were observed to be small or insignificant. Our observers adapted to intense homogenous, foveal fields of linearly polarized, orange-red light produced by a beam that entered the side of the pupil. Periodically the plane of polarization of the beam suddenly shifted 90 degrees without there being any change in the spectral distribution of the light or position of the beam in the pupil plane. The change of radiance of the beam could be adjusted to be as low as approx. 0.5%. Signal detection experiments revealed that observers typically could not detect a change of polarization of the field. Results obtained with the method of adjustment showed that the threshold of an increment flash presented on the intense field was not affected by changing the polarization of the field. Physiological implications of these results are discussed.

Adaptation, Ocular↗

PubMed1982

Low spatial-frequency channels in human vision: adaptation and masking.

Previous work showed that adapting to low spatial frequency gratings (below 1.5 cycles/degree) may cause maximal spatial adaptation at a significantly higher spatial frequency. It has been suggested that there are no adaptable spatial-frequency channels tuned to below 1.5 c/deg. Contrary to this view, we found that adaptation and masking with low spatial frequencies (0.12-1.0 c/deg) produced maximal threshold elevations when the test patterns were the same spatial frequency as the adapting or masking pattern. These results were obtained using test patterns that turned on and off gradually or sharply. The results suggest that there are form mechanisms optimally sensitive to very low spatial frequencies. Adaptation was selective to position (phase) and orientation at low spatial frequencies; masking was observed to be selective to orientation at a spatial frequency as low as 0.2 c/deg. A clear dichotomy between transient, motion channels and sustained, form channels at low spatial and temporal frequencies may represent an unrealistic simplification. There may exist directionally-selective motion mechanisms sensitive to very slow motion, and these may play a role in the discrimination of form. The discussion considers the bandwidths of the low spatial frequency mechanisms.

Adaptation, Ocular↗

PubMed1981

A 'ready' food system that works.

Explore the source record for details and available documents.

California↗

PubMed1980

Individual variation of centric heterochromatin in man.

Explore the source record for details and available documents.

Adult↗

PubMed1979

Chlormethiazole treatment and breast feeding.

Four mothers receiving chlormethiazole for pre-eclampsia and their babies were the subjects of the investigation. Blood samples at delivery and blood and breast milk samples in the postpartum period were analysed for chlormethiazole. Concentrations ranged from 1.340 to 1.640 micrograms/g of sample of umbilical artery blood at birth, and fell to 0.010 to 0.153 micrograms/g in capillary blood 20 to 26 hours later. After the start of breast feeding, chlormethiazole in the babies was detectable in only 3 out of 27 serial blood samples and was 0.018, 0.009 and 0.006 micrograms/g. The highest calculated amount of chlormethiazole ingested at a breast feed was 37.2 micrograms. It is suggested that breast feeding should not be delayed solely on account of chlormethiazole therapy.

Breast Feeding↗

PubMed1978

Form-colour aftereffects: selectivity to local luminance contrast.

For long periods observers fixated low spatial frequency coloured gratings. Black and white test gratings of the same spatial frequency and orientation as the adapting gratings appeared coloured with the hue complementary to the adapting patterns when the dark test stripes fell on retinal areas previously occupied by the dark adapting stripes; no colour or very weak colour was seen when the test gratings were reversed in phase (contrast reversed). No colour aftereffects were produced with coloured gratings that lacked luminance contrast. The selectivity to the polarity of local luminance contrast can be explained by mechanisms that respond conjointly to colour and luminance contrast. The aftereffects are selective to spatial phase.

Afterimage↗

PubMed1978

Form aftereffect contingent upon a colour shift.

After prolonged fixation of coloured gratings of low spatial frequency, images of the gratings can be elicited up to 90 min thereafter when the colour of a spatially homogeneous test field is suddenly changed. Only adapting gratings with luminance contrast induce clear aftereffects. Control experiments rule out afterimages as an explanation of the aftereffects.

Adaptation, Ocular↗