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Trading Noise for Stimulus Duration in Orientation Judgments
Kei Kurosawa, Kristen Strong & Nestor Matthews
Department of Psychology, Denison University, Granville OH 43023 USA
Results
Motivation
Earlier studies showed that our ability to judge a subtle angular
difference increases over the tens of milliseconds following
stimulus presentation1, and that there may be greater neural noise
at oblique (diagonal) axes than at cardinal (horizontal) axes2.
Here we investigated the extent to which stimulus duration can be
traded for orientation noise when judging angular differences.
Experiment 1
Experiment 2
Method
Exp 1 – Participants foveally viewed two sequentially
we varied the movie duration (42 - 142 msec), and varied the
noise bandwidth (0 – 60 deg) around a cardinal axis only.
In Exp1, orientation sensitivity grew with decreases in noise
bandwidth. At the greatest bandwidths, orientation sensitivity
was poor and was comparable at the cardinal and oblique
axes, although performance was reliably better than chance at
each axis. The oblique effect (OE) emerged only as the noise
bandwidth decreased. This is similar to previous work1 that
showed that the OE emerges with increasing stimulus duration.
Exp 2 revealed a trade-off between noise bandwidth and
stimulus duration. Increases in noise bandwidth effectively
canceled the enhancements in orientation sensitivity that
occurred with increasing stimulus duration.
presented grating-movies with bulls-eye masks preceding and
following each movie. The task was to judge the mean
orientation of the second movie as clockwise or anti-clockwise
to the first (figure below). With the movie duration fixed at 108
msec and a mean difference of ~3 deg between the two movies,
the axis (cardinal or oblique) and the bandwidth of orientation
noise (0 - 60 deg) were randomly varied across trials.
Exp 2 – The procedure was the same as in Exp 1 except that
Discussion
Experiment 3
In Exp 3, participants judged the bandwidth range rather than
the mean orientation. The data indicated that an OE was absent
at each bandwidth condition. The OE for range judgments was
absent in EXP 3 even when the stimuli were identical to those
that generated an OE for mean judgments (Exp 1). Because
identical stimuli would create identical responses in the neurons
that detect orientation, the OE must originate after orientation is
detected in the visual system.
Exp 3 – The first movie on each trial had a randomly selected
bandwidth (10 - 90 deg). The noise bandwidth of the second
movie randomly increased or decreased by 10 – 50% relative to
the first. Participants judged whether the second orientationbandwidth was narrower or broader than the first.
The Bottom Line
The findings suggest that orientation sensitivity arises from axisspecific noise reductions over time, with the oblique effect
originating after the stage at which orientation is detected.
References
1.
2.
Matthews, Rojewski & Cox (2005) PMID 15929646.
Heeley, Buchanan-Smith, Cromwell & Wright (1997) PMID 9068823.
This poster can be viewed and downloaded at
http://www.denison.edu/~matthewsn/noise05.html