Journal of Vision (2007) 7(8):1, 1-12
Schofield, Ledgeway, & Hutchinson
between cues and, for completeness, the transfer of other
types of adaptation. Lu, Sperling, and Beck (1997, but see
also Lu & Sperling, 2001) found selective MAEs for first-,
second-, and third-order motion (LM, CM, and motion-
from-motion respectively) with little transfer of adaptation
between cue types. Nishida, Ledgeway, and Edwards
(1997) measured direction-identification thresholds for
LM and CM stimuli and found strong postadaptation
threshold elevation that was direction, spatial frequency,
and cue specific; the only transfer observed was very weak
and not spatial frequency tuned.
In contrast to the studies above, some researchers have
found good transfer of adaptation between cues. Nishida
and Sato (1995) used a variety of second- and third-order
adaptation stimuli but tested for the dMAE using flickering
luminance gratings; their results suggest that the dMAE
can transfer from higher order cues to the first-order
motion system. Further, Georgeson and Schofield (2002)
found good transfer of the tilt and contrast-reduction
aftereffects between static LM and CM stimuli. Note that,
as with their moving counterparts, there is considerable
evidence to suggest that static LM and CM signals are
detected independently (Georgeson & Schofield, 2002;
Schofield & Georgeson, 1999). Similarly, Cruickshank
(2006) and Cruickshank and Schofield (2005) have
demonstrated partial transfer of the tilt and contrast-
reduction aftereffects between CM and OM, despite
evidence to support their independent detection (Kingdom
et al., 2003; Schofield & Yates, 2005). However,
Cruickshank was unable to find transfer of the contrast-
reduction aftereffect between CM and disparity modula-
tions or between OM and disparity modulations.
In this article, we test the spatial-frequency tuning of
any observed aftereffects. Spatial-frequency tuning can be
taken as the signature of a channel-like mechanism. Also,
it can be informative to compare the tuning of any
transferred aftereffects to the tuning of the within-cue
effects. However, comparing spatial-frequency tuning
across conditions presupposes that the dMAE is a tuned
effect. Ashida and Osaka (1994) found that dMAE did not
exhibit spatial-frequency tuning. In contrast, others have
found that the dMAE can be well tuned for spatial
frequency (Bex, Verstraten, & Mareschal, 1996), although
the sharpness of this tuning reduces with increased (test)
temporal frequency (Mareschal, Ashida, Bex, Nishida, &
Verstraten, 1997). Accordingly, we tested at a relatively
low temporal frequency (1 Hz).
Experiments 1 and 2: Spatial and
temporal sensitivity_____________
The spatiotemporal frequency response of the human
visual system to moving OM stimuli has yet to be
characterized. We now address this issue as a necessary
prerequisite to our adaptation study. We also measured
sensitivity for LM and CM so as to allow direct comparison
with OM under the same test conditions. These functions
facilitated our choice of spatial and temporal frequency in
our adaptation experiment and allowed us to equate the
visibility of our cues for each observer.
Methods
Observers
Four observers participated overall, with three observers
in each experiment. All had normal or corrected-to-normal
visual acuity. Observers A.J.S., C.V.H., and P.D.J. (the first
two are authors of this study, whereas the latter is a paid
volunteer who was naBve to the purpose of the experiment)
participated in Experiment 1. In Experiment 2, observer
P.D.J. was unavailable and T.L. (an author of this study)
acted as the third observer.
Apparatus and stimuli
Stimuli were generated using a Macintosh G4 computer
and presented on a Sony Trinitron GDM-520 monitor
(refresh = 75 Hz) using custom software written in C. The
number of intensity levels available was increased from
256 to 16,384 using a Cambridge Research Systems
Bits++ attenuation device in its Mono++ mode to produce
“grayscale” images on the color monitor. The monitor was
gamma corrected using a sensitive, motion-nulling psy-
chophysical task (Gurnsey, Fleet, & Potechin, 1998;
Ledgeway & Smith, 1994a; Lu & Sperling 2001; Nishida
et al., 1997). Stimuli were presented within a 5.3 deg
square window at the center of the display. The mean lumi-
nance of the window and the remainder of the display area
(which was homogeneous) was approximately 55 cd/m2.
The viewing distance was 2.08 m. Viewing was binocular,
and a prominent fixation spot was located at the center of
the display to aid stable fixation and discourage ocular
tracking of the motion stimuli.
All stimuli were drifting sinusoidal modulations of
either first-order or second-order motion that were oriented
horizontally in space (see Movies 1-3). A dynamic noise
carrier was used in all cases to allow direct comparisons
between the results for each stimulus type. The carrier was
a field of one-dimensional (1-D), vertically oriented,
dynamic, random, binary visual noise. The noise had a
Michelson contrast of 0.25 and was replaced with a new
stochastic sample each time the position of the drifting
modulation signal was updated, at a rate of 37.5 Hz. Noise
stripes subtended 0.625 arcmin of visual angle.
First-order (LM) motion patterns were constructed by
adding a drifting sinusoidal luminance grating to the field
of dynamic noise. Second-order motion patterns were
constructed as follows. For CM, the amplitude of the noise
carrier was modulated by a drifting sinusoidal waveform
(see Schofield & Georgeson, 1999). To generate OM