Development of Orientation Tuning in the Visual Cortex of Kittens
Orientation tuning of single units in striate cortex of kittens aged 2–6 weeks was measured quantitatively. Results are based on 227 visually responsive units from 36 kittens of which 9 were reared in complete darkness. Cells were classed as non-oriented (N.O.), orientation-biased (O.B.), and orientation-selective (Or.) using objective criteria. Specificity of O.B. and O.S. cells was gauged using the half-width of the orientation tuning curve at half the maximum response amplitude.
In 2-week-old kittens, O.B. and O.S. cells comprised 41% and 38% of the total (responsive) sample (N = 39), respectively. By 5 to 6 weeks of age, O.B. represented 10% and O.S. 86% of the sample (N = 61), with intermediate ages showing a roughly linear progression between the two levels. In contrast, dark-reared animals of up to 6 weeks of age retained distributions nearly identical with that seen at 2 weeks. Orientation specificity of cells in normally reared kittens improved from a mean of 29° at 2 weeks to essentially adult performance (19°) at 5 and 6 weeks. For the dark-reared kittens this figure remained essentially static through 6 weeks of age.
Discounting such factors as optical blur (the justification of which will be discussed), it may be concluded that visual experience plays a major role in refining the neural mechanisms responsible for orientation selectivity. Moreover, total visual deprivation “freezes” both the number and specificity of oriented cells at the level found in very young kittens.
KeywordsReceptive Field Visual Experience Tuning Curve Striate Cortex Orientation Selectivity
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