A white-noise analysis of responses and receptive fields of catfish cones.

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Abstract
Responses and receptive fields of catfish [Ictalurus-punctatus] cones were studied using classical flash stimuli, white-noise-modulated spots and annuli, and a pseudorandom-width bar grating stimulus. The cone''s response to a flashed stimulus is, in most cases, a maintained hyperpolarization lasting for the duration of the stimulus. A modified equation of the Michaelis-Mention form defines the cone''s V-log I curve. The incremental sensitivity of the cone was the local slope of the Michaelis-Menton curve. The catfish cone responds as a linear, low-pass spatial and temporal filter. Signal transmission between cone and horizontal cell is linear and shows little evidence of filtering. Feedback from horizontal cells to cones was active under certain stimulus conditions. The feedback appears to be different from that previously described in other species. It cannot be wholly characterized as negative feedback. A 2-state type of feedback is proposed to account for the results.