2 results
Orientation and Direction Tuning of Goldfish Ganglion Cells
- Joseph Bilotta, Israel Abramov
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- Journal:
- Visual Neuroscience / Volume 2 / Issue 1 / January 1989
- Published online by Cambridge University Press:
- 02 June 2009, pp. 3-13
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- Article
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Orientation and direction tuning were examined in goldfish ganglion cells by drifting sinusoidal gratings across the receptive field of the cell. Each ganglion cell was first classified as X-, Y- or W-like based on its responses to a contrast-reversal grating positioned at various spatial phases of the cell's receptive field. Sinusoidal gratings were drifted at different orientations and directions across the receptive field of the cell; spatial frequency and contrast of the grating were also varied. It was found that some X-like cells responded similarly to all orientations and directions, indicating that these cells had circular and symmetrical fields. Other X-like cells showed a preference for certain orientations at high spatial frequencies suggesting that these cells possess an elliptical center mechanism (since only the center mechanism is sensitive to high spatial frequencies). In virtually all cases, X-like cells were not directionally tuned. All but one Y-like cell displayed orientation tuning but, as with X-like cells, orientation tuning appeared only at high spatial frequencies. A substantial portion of these Y-like cells also showed a direction preference. This preference was dependent on spatial frequency but in a manner different from orientation tuning, suggesting that these two phenomena result from different mechanisms. All W-like cells possessed orientation and direction tuning, both of which depended on the spatial frequency of the stimulus. These results support past work which suggests that the center and surround components of retinal ganglion cell receptive fields are not necessarily circular or concentric, and that they may actually consist of smaller subareas.
4 - Physiological mechanisms of color vision
- Edited by C. L. Hardin, Syracuse University, New York, Luisa Maffi, University of California, Berkeley
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- Book:
- Color Categories in Thought and Language
- Published online:
- 20 August 2009
- Print publication:
- 14 August 1997, pp 89-117
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Summary
Color vision in general
Our world appears brightly colored, the colors – “natural” or artificial – drawn from huge palettes of pigments, dyes, and lights. But despite the ubiquity of color and the many studies of it, our knowledge of color is still filled with surprising gaps and misconceptions. Part of the problem is that there is no one “correct” way to ask about color: we each approach it with the preconceptions of our different disciplines. To bolster our “givens,” we show how they accord with “facts” from neighboring disciplines. For example, linguists have been known to justify some of their conclusions by showing that they agree with the known categories of neuronal responses delineated by physiologists (e.g. Berlin and Kay 1969; Kay, Berlin, and Merrifield 1991), and physiologists have returned the compliment by referring to the universal color categories discovered by the linguists (e.g. Ratliff 1976, 1992). Unfortunately each of the many approaches to color vision has its own set of unvoiced problems. My role is both to describe some of the physiological mechanisms that might underlie color vision and to uncover some of the skeletons hidden in my discipline's intellectual closets. (See Abramov and Gordon 1994 for a detailed treatment of many of these issues.)
Since color is a response of the nervous system to certain stimuli, the goal is to answer the question, “How does the human nervous system encode those aspects of the stimulus that elicit color sensations?” Obviously much of the work I describe is done on nonhuman species.