Colin Blakemore

Lateral inhibition between orientation detectors in the cat's visual cortex.

Ncurones in the visual cortex of higher mammals respond very selectively to white or black bars at particular orientations in the visual field (Hubel and Wiesel, 1962, 1968). Psychophysical experiments in man have led several authors to suggest that there is mutual inhibition between detectors with slightly different preferred orientations (Andrews, 1965; Blakemore et al., 1970). We now have physiological evidence for such inhibition in the cat.

Innate and environmental factors in the development of the kitten's visual cortex.

1. This is a study of the receptive fields of 771 cells recorded in the visual cortex of twenty‐five kittens reared normally or subjected to various kinds of visual deprivation or environmental manipulation. 2. Kittens deprived of patterned visual experience, by dark rearing or diffuse occlusion of the eyes, have a majority of cirtical neurones with little or no specificity for the orientation or axis of movement of visual stimuli. However, in such deprived animals, especially those younger than 3 weeks, there are a number of genuinely orientation selective cells. They are broadly turned (by adult standards), they are almost always of the simple type, are heavily dominated by one eye, and are found mainly in the deeper layers of the cortex, especially layer IV. 3...

Size Adaptation: A New Aftereffect

If, after prolonged observation of a striped pattern, one views a grating of the same orientation with somewhat narrower bars, then the bars seem even thinner than in fact they are. Broader bars seem broader still. This finding implies a system of size-detecting channels in humnan vision. The phenomenon may underlie many of the classical figural aftereffects.

Interactions between orientations in human vision

SummarySingle lines cause changes in the apparent orientation of nearby lines of somewhat different orientation: acute angles are perceptually expanded while obtuse angles apparently contract. This phenomenon is measured by a matching technique and evidence is presented that it is due to recurrent, inhibitory interactions among orientation selective neural channels. In particular, a third line added to an angle figure can have a disinhibiting effect on the orientational distortion. Orientation selective channels maximally sensitive to different orientations may have different distributions of inhibitory input in the orientation domain. The results are interpreted in terms of the organization of neurones in the visual cortex. Each cell may receive a crude orientation selectivity from its direct input, and be inhibited, over an even broader range of orientation, by neurones in the same column and adjacent ones.

The orientation specificity of two visual after-effects.

1. Inspection of a high‐contrast adapting grating produces two visual after‐effects: (a) the contrast threshold is raised for test gratings of similar spatial frequency to that of the adapting pattern and (b) the apparent spatial frequency of test gratings shifts away from that of the adapting grating—higher frequencies seem higher and lower ones lower than they really are.

Stimulus specificity in the human visual system

During adaptation to a high contrast grating it gradually seems to fade. A lower-contrast test grating appearing directly after the adapting pattern appears reduced in apparent contrast. The orientation specificity and spatial frequency specificity of thisapparent contrast reduction have been determined by adapting to gratings of various orientations and spatial frequencies, and measuring the contrast reduction for test gratings of fixed orientation and frequency. The sensitivity characteristic for orientation has a half-width at half amplitude of 8°: that for spatial frequency has a full-width at half amplitude of 0.75 octaves. This result is compared with the properties of neurones in the cat and monkey visual cortex.

An analysis of orientation selectivity in the cat's visual cortex

SummaryThe responses of cells in the cats visual cortex to a moving bar of light have been analysed quantitatively, using an integration of the post-stimulus time histogram, with particular reference to orientation selectivity. The method is assessed as to its reliability and usefulness; it is shown that much precise information about a cell can be derived from its orientational tuning curve.Complex cells were found on average to show more spontaneous activity, greater response amplitude, and slightly broader orientational tuning, than either simple or hypercomplex cell types. Correlations between spontaneous and evoked activity and orientational selectivity give information as to the possible mechanisms of excitation and inhibition of the cells. The question of meridional variations in perception has been especially examined: the unexpected finding that many simple cells detecting orientations close to horizontal or vertical are very narrowly tuned, which is not the case for complex or hypercomplex cells, is discussed in relation to human psychophysical variations in orientation discrimination and contrast sensitivity.

The perceived spatial frequency shift: evidence for frequency-selective neurones in the human brain

1. Prolonged observation of a high‐contrast grating pattern causes an apparent shift in the spatial frequency of gratings subsequently viewed with the same retinal region. Gratings of higher and lower frequency than the adapting pattern seem, respectively, higher and lower than in fact they are.

A second neural mechanism of binocular depth discrimination

1. Rotation of an object about its horizontal axis, towards or away from the viewers eyes, usually causes the images of its contours to have slightly different orientations on the two retinae.

Interocular Transfer in Normal Humans, and Those Who Lack Stereopsis

Interocular transfer of the tilt aftereffect was investigated in normal humans with good stereopsis and in subjects without stereoscopic vision. These latter subjects were divided into two groups: those with and those without a history of strabismus. Strabismic subjects showed grossly reduced interocular transfer of the effect (12% mean transfer). Nonstrabismic subjects had moderate transfer (49%) and normal subjects showed approximately 70% mean transfer. All normal subjects showed greater transfer from the dominant eye to the nondominant than vice versa. The results are discussed with respect to developmental effects in the visual system of cats and humans, and the nature of the tilt aftereffect.