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Up-down Asymmetries in Speed PerceptionWe compared speed matches for pairs of stimuli that moved in opposite directions (upward and downward). Stimuli were elliptical patches (2 deg horizontally by 1 deg vertically) of horizontal sinusoidal gratings of spatial. frequency 2 cycles/deg. Two sequential 380 msec reveal presentations were compared. One of each pair of gratings (the standard) moved at 4 Hz (2 deg/sec), the other (the test) moved at a rate determined by a simple up-down staircase. The point of subjectively equal speed was calculated from the average of the last eight reversals. The task was to fixate a central point and to determine which one of the pair appeared to move faster. Eight of 10 observers perceived the upward drifting grating as moving faster than a grating moving downward but otherwise identical. on average (N = 10), when the standard moved downward, it was matched by a test moving upward at 94.7+/-1.7(SE)% of the standard speed, and when the standard moved upward it was matched by a test moving downward at 105.1+/-2.3(SE)% of the standard speed. Extending this paradigm over a range of spatial (1.5 to 13.5 c/d) and temporal (1.5 to 13.5 Hz) frequencies, preliminary results (N = 4) suggest that, under the conditions of our experiment, upward matter is seen as faster than downward for speeds greater than approx.1 deg/sec, but the effect appears to reverse at speeds below approx.1 deg/sec with downward motion perceived as faster. Given that an up-down asymmetry has been observed for the optokinetic response, both perceptual and oculomotor contributions to this phenomenon deserve exploration.
Document ID
20020049822
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Thompson, Peter
(NASA Ames Research Center Moffett Field, CA United States)
Stone, Leland S.
(NASA Ames Research Center Moffett Field, CA United States)
Date Acquired
August 20, 2013
Publication Date
January 1, 1997
Subject Category
Physics (General)
Meeting Information
Meeting: 1997 European Conference on Visual Perception
Location: Helsinki
Country: Finland
Start Date: August 25, 1997
End Date: August 29, 1997
Funding Number(s)
PROJECT: RTOP 548-50-12
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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