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Linear combinations of signals from two lines of the same or different orientations.

Abstract：

:Whereas the influence on the elevation of visually perceived eye level (VPEL) by two bilaterally symmetric, long (64 degrees-long), pitched-from-vertical lines in total darkness is only a little more than the average of the VPELs of the two lines measured separately [Matin & Li (1999). Vision Research, 39, 307-329], in the present experiments with 49 2-line combinations of seven orientations (-30 degrees to +30 degrees pitch), the VPEL for two short (12 degrees-long) lines equals the additive sum of the separate influences of the two lines. With one line at a fixed orientation, the slope of the VPEL-versus-pitch function with the second line variable equals the slope of the function when viewing one line alone, but is shifted from the 1-line-alone function by the magnitude of the VPEL of the fixed line. Both the near-averaging and the additivity are summarized by V(theta l, theta r) = k1 + k2 [V(theta l) + V(theta r)], where V(theta l) and V(theta r) are the 1-line VPELs for the pitches of the left and right lines, and V(theta l, theta r) is the 2-line VPEL; the slope constant k2 equals 0.5 for averaging, and 1.00 for simple additivity of the separate visual influences. Measured values are k2 = 0.99 and k2 = 0.61 for short and long lines, respectively. The shift of slope constant is determined by line length and not orientation: parallel and nonparallel lines follow the same rules of combination for short lines as they do for long lines. As for long lines, the short-line results are clear in showing that the visual influence on VPEL is controlled by an opponent-process mechanism. Although 'saturation-near-an-asymptote' along with opponency are required components of the interpretation for the basis of the combination of lines of different orientations and different lengths, they are not by themselves sufficient: All results conform to a neurophysiologically-based model [Matin and Li (1997b). Society for Neuroscience, 23, 175; Matin & Li, under review] that parallel processes feedforward signals from orientation-selective neural units in V1; the model accounts for the shift from additivity to near-averaging with increase in line length as a consequence of the increased contribution of shunting.

journal_name

Vision Res

journal_title

Vision research

authors

Matin L,Li W

doi

10.1016/s0042-6989(99)00182-0

subject

Has Abstract

pub_date

2000-01-01 00:00:00

pages

517-27

issue

eissn

0042-6989

issn

1878-5646

pii

S0042-6989(99)00182-0

journal_volume

pub_type

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Linear combinations of signals from two lines of the same or different orientations.