Sustained and transient responses by cat striate cells to stationary flashing light and dark bars

In human vision there are two distinct thresholds for a temporally modulated spatial stimulus, one for the detection of flicker by movement and the other for the recognition of spatial structure of patternV,9,1a,tL Keesey 7 and Tolhurst t4 proposed that the two thresholds represent the activities of two separate sets of neurons: one transmitting temporal changes and the other sensitive to spatial contrast. Subsequently, Kulikowski and Tolhurst u found that the proposed movement-detectors are sensitive to a transient change in contrast, whereas the pattern detectors invariably respond to the sustained contrast itself. These detectors can be compared to the transient (Y) and sustained (X) neurons respectively in the cat visual system 1,3,13. but Kulikowski and Tolhurst 11 have noted serious quantitative discrepancies in their corresponding characteristics: X (sustained) cells respond too transiently to provide exclusive inputs to 'sustained' pattern detectors. The present investigation was designed to test which neuronal responses could convey information about a change in contrast or the contrast itself. For a general account of our methods see Nelson, Kato and Bishop ~z. Cats were anaesthetized with halothane, N20 and 02 for surgery and all wounds were infused with a long-acting local anaesthetic. For recording the animals were anaesthetized with N20-O2 (70:30) and paralyzed with Flaxedil and toxiferine. The stroke volume of artificial respiration was adjusted to keep the end-tidal CO2 concentration at 4 9/0 and the EEG was usually monitored continuously. Stimuli consisting of light and dark bars or edges and sine wave gratings of adjustable contrast were electronically generated on an oscilloscope screen (Tektronix type 604 with P31 phosphor)placed at 63 cm from the cat 's eyes. In particular 3 modes of stimulation were used. For each mode the transient change in contrast was the same ( A C -0.2), whether the contrast

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