Induction of novel colour categories in a
non-categorical colour space
Belinda Gargaro, Simon Cropper and Michael
Johnston
belinda_gargaro@hotmail.com
The category boundary effect (CBE) is an increase in discriminability
across a perceptual boundary relative to that within a category. This study
quantified the CBE for pre-existing and novel categories within a
non-categorical (cardinal) colour space. This required the following five
stages: 1) Four observers freely categorised the equiluminant
plane of cardinal space. This allowed the identification of subjective category
and boundary regions. 2) Discrimination was measured within and across
subjective categories. No CBEs were apparent for any observer. 3) A subjective
category was selected and a novel boundary induced through training.
4) Discrimination was retested as in stage 2. Once again no CBEs were
found. 5) After no less than four weeks observers repeated stage 1. Free
categorisation revealed the presence of the induced novel categories suggesting
categorical colour perception in the absence of any CBEs.
Monocular texture and binocular slant
Barbara Gillam, Tatjana
Seizova-Cajic and Michael Pianta
b.gillam@unsw.edu.au
We show how the presence of monocular texture at the sides of random dot
stereograms of a horizontally slanted surface
provides potential information about the slant as well as the azimuth of the
surface. Experiments were conducted to compare the use of this information when
the monocular texture was consistent with part of the background, with an
aperture in front of the surface and with a mixture of the two. Only the latter
two conditions gave a significant enhancement of slant relative to the
disparity gradient alone and this enhancement was found to decrease with the
width of the surface and increase with the disparity gradient. The sidebands
alone had little effect on slant. The reasons for these results will be
discussed. It is concluded that the process underlying slant enhancement
differs from Panum's limiting case and that it
involves an interaction of the monocular sidebands with the disparity gradient
rather than the addition of a separate cue.
Luminance and contrast as depth cues
Donovan G. Govan and Robert P. O'Shea
nemesis@psy.otago.ac.nz
Sunday, Commerce 2.20, 11.30 am
It has long been held that luminance acts as a cue for depth perception.
But varying the luminance of a stimulus inevitably alters its contrast with its
background. Recent research shows that contrast is a depth cue. I have
distinguished two kinds of contrast, external contrast, the contrast of a
stimulus with its background, and internal contrast, the contrast within the
stimulus. Four observers reported the relative depth of two squares filled with
horizontal sine-wave gratings. Their luminances and
internal contrasts were varied along with the luminance of their background.
We found internal and external contrast to be additive effects, whereby
the stimulus with either a higher internal or external contrast appeared
nearer. When the internal and external contrast of the squares was equated,
luminance acted as an ambiguous cue, with the darker square appearing nearer
for three of the four observers and farther for the other.
A limit to the perception of transparent motion based
on signal-to-noise processes
John A. Greenwood and Mark Edwards
mark.edwards@anu.edu.au
Transparent motion occurs when two or more different motion signals are
present within the same region of space. Aim: To determine the number of
transparent motion signals that can be represented simultaneously by the visual
system and the processes underlying this limit. Task: Observers indicated which
of 2 temporal intervals contained the highest number of signal directions.
Results: For short stimulus durations, observers could perceive a maximum of 2
signals simultaneously, even though all signal intensities were above
unidirectional thresholds. When signal intensities in the 2-signal condition
were reduced to those used in the 3-signal condition, performance declined
markedly. Further, 3 signals could be perceived when the signals drove
different speed-tuned global-motion mechanisms. Conclusions: Transparency
limits are based upon signal-to-noise processes at the global-motion stage,
with the thresholds required to detect transparent signals being higher than
those required for unidirectional signals.
Monocular transparency is not a new form of unpaired stereopsis
Phillip M. Grove, K. R. Brooks, B. L. Anderson and B. J. Gillam
p.grove@unsw.edu.au
Howard and Duke (2003) generated stereograms
with a grey transparent square offset from a vertical bar in one eye, and a
vertical bar with a gap in the other eye. They argued that these displays were
"without conventional disparity" and that the metrical depth
experienced was a new form of unpaired stereopsis due
to "transparency rather than occlusion". Another possibility is that
the perceived depth in these displays was obtained from horizontal contours. To
test this possibility, we generated three displays that contained similar
horizontal contour terminations, but were inconsistent with transparency.
Reliable depth was seen in all stimuli. We conclude that in our stimuli,
and those of Howard and Duke, transparency is not responsible for the
perception of depth, which appears to be based instead on disparate horizontal
contour terminations. Our results also show that disparate contours of opposite
contrast polarity can generate depth.
Explicit reasoning impairs judgements of Olympic dives
Jamin Halberstadt and James Green
jhalbers@psy.otago.ac.nz
Previous research has established that providing reasons for one's
attitudes prior to reporting them changes the attitudes for the worse, but
"attitude quality" has been difficult to validate. In the current
study reasoners' and nonreasoners'
assessments of Olympic dives were compared to the ratings they received by the
Olympic judges. Reasoners' ratings, particularly of
poorer dives, corresponded worse to those of judges, even when rating them a
second time under control conditions, and did not vary with individual
differences in decision-making style.
The influence of illusory line motion on saccadic
latency
Jeff Hamm1, Trevor Crawford2 and Matthew Kean1*
m.kean@auckland.ac.nz
Peripheral flashes are known to automatically attract visual attention.
If a static bar is presented with one end near the flash, illusory line motion
(ILM) is perceived away from the flashed location. Prior research has shown
that visual attention will track this illusory motion. Further, it is generally
accepted that visual attention is directed to a location in space prior to the
execution of a saccade to that location. If ILM draws attention away from the
flash and towards the non-flashed location, this should slow prosaccades - which are normally rapidly initiated - and
speed antisaccades - which are normally comparatively
slow. (Here, prosaccades and antisaccades
are defined in reference to the location of the ILM-inducing flash). Pilot
results have supported the predictions. Experimental data will be presented
which explore this phenomenon further.
Putting orientation in the picture: A new theory of
object recognition
Irina M.
Harris and Paul E. Dux
iharris@maccs.mq.edu.au
Recognition costs incurred by rotated objects have often been
interpreted as evidence for viewpoint-dependent recognition. We review findings
which suggest that recognition is actually mediated by orientation-invariant
representations and that the viewpoint-dependent effects reflect a
post-recognition process of determining the object’s orientation in space. This
idea is articulated in a two-stage theory of object recognition. During the
first stage, the object’s identity is established by activating an object
representation stored in memory. Strictly speaking, this is the recognition
process, and is achieved via orientation-invariant means. However, for an
object to be consciously perceived, a second stage of processing is necessary,
in which the recovered identity is bound to orientation information in order to
deliver a stable percept anchored in space and time.
Depth from monocular half images: Occlusion or low
level processing?
Julie M. Harris, Laurie Wilcox and Suzanne McKee
University of Newcastle upon Tyne, York University,
Smith-Kettlewell Eye Research Institute
j.harris@ncl.ac.uk
Depth can be perceived when a single point or object is viewed in one
eye, without a partner point in the other eye (Kaye, 1978). Why? We
considered two models. First, monocular points in an image are consistent with
occlusion situations, such as when viewing a step edge. Second, only rarely
(for fixation along the midline) do points matched on the temporal (nasal)
retina not have a nasal (temporal) match in the other eye. Could the depth seen
be due to a specialised mechanism for seeing depth along the midline? We
explored this by measuring depth identification using both stereoscopic and
monocular half-images. We assessed the effect of interocular
contrast and midline vs. eccentric fixation, on perceived depth. Results are
not consistent with a high-level occlusion explanation, but could be explained
by a coarse low-level mechanism which matches the monocular half-image to noise
in the signal from the other eye.
Dissociating detection from localisation of tactile
stimuli
Justin Harris, Thida Thein
and Colin Clifford
justinh@psych.usyd.edu.au
Neurological studies (including two reports of "tactile blindsight") suggest that detecting and locating
tactile stimuli are doubly dissociable processes, presumably mediated by
different neural structures. We sought evidence for such a
dissociation in neurologically intact participants. We compared people's
accuracy at detecting versus locating a backward-masked stimulus presented to
one of four fingers. When accuracy scores were converted to a bias-free measure
of sensitivity (d_), subjects were found to be better at detecting than
locating the stimulus. Detection was also more susceptible than localization to
manipulations involving the mask: detection improved more than localization as
the target-mask interval increased; and detection, but not localization, was
affected by changes in mask frequency. Comparing these results with simulated
data generated by computational models, we conclude that detection and
localization are not mutually independent, as previous neurological studies
might suggest, but rather localization is subsequent to detection in a
serially-organized sensory processing hierarchy.
Pseudoneglect in the 'mental
number line'
Markus Hausmann
Markus.Hausman@rub.de
The left and a right hemispace are integrated
by the brain to a complete representation. This spatial mapping seems not to be
veridical but slightly distorted to the left of the objective midline, most
likely as a result of a superiority of the right brain in spatial awareness.
This can be measured with a visual line bisection task. When normal subjects
bisect horizontal lines they deviate to the left of the veridical center. Line length, line position, scan direction and many
other factors strongly affect the line bisection bias. Using a mental line,
that is the mental number line, it is shown that the leftward distortion is not
due to physical properties of the percept. The results strongly support
the notion that numbers are represented mentally from left to right, and
indicate that the directional bias in bisecting physical lines is
representational in origin.
Configural processing in own-race and other-race face
recognition
William G.
Hayward1, Hoi-Yan Lam1, Keung-Tat Lee1, Gillian Rhodes2,
Rebecca Glauert2, Emma Jaquet2 and Elinor
McKone3
whayward@psy.cuhk.edu.hk
Many studies of expertise in face recognition have found evidence for configural processing in recognition of own-race faces.
However, few studies have examined whether recognition of other-race faces
shows a corresponding reduction in sensitivity for configural
information. In Experiment 1, we found that Australian participants showed
greater configural sensitivity for Caucasian than
Chinese faces; however,
Why we see illusory relative motion between abutting
gratings
Trevor Hine
t.hine@griffith.edu.au
Saturday, Commerce 2.21, 9.30 am
A simple stimulus comprising two abutting stationary gratings can
produce a strong illusion of segmentation by relative motion. A theory of this
effect is developed based upon the well-known fact that the perception of
motion of entire objects in the visual field arises from the integration of
local motion signals. It takes into account that the accuracy of these signals
is contaminated by noise: whether the noise is neural or statistical, that is
the motion signal is small (for example, as in fixational
eye movements) compared to the resolution of the motion detector. The model is
used to explain parametric data from experiments using the simple stimulus.
Results for optimal angle (at least 120 deg between local motion directions),
velocity (< 4 deg/ sec) and spatial frequency (6 - 8 cpd)
are predicted. Other theories (e.g., Fermüller
et al. (2000) fail to predict these and other results from the simple
stimulus. The theory presesented here can
be extended to explain illusory relative motion in other patterns, such as the Ouchi.
Antje
Hollander1, Markus Hausmann1, Jeff P. Hamm2
and Michael C. Corballis2
Ruhr-University Bochum1, Universityof Auckland2
antje.hollaender@web.de
Differences in functional cerebral asymmetries modulated by gonadal steroid hormones were examined during the menstrual
cycle in women. Women were tested with a double-stream rapid serial visual
presentation (RSVP) task, with one stream in each visual field, during the low
steroid menses and the high steroid midluteal phase. They
were required to detect a target item, and then a probe item, each of which
could appear in either stream. If the probe appeared 200-500 ms after the
target, its detection was impaired-a phenomenon known as the "attentional blink." This occurred in both streams
in the midluteal phase, but only in the right visual
field in the during menses. Thus low steroid levels
appeared to restrict the attentional blink to the
left hemisphere, while high levels of estradiol and
progesterone in the midluteal phase appeared to
reduce functional asymmetries by selectively increasing the attentional
blink in the right hemisphere.
Sex differences in the salience of spatial cues used
by rats in detection of a brightness change
Rob N. Hughes
rob.hughes@canterbury.ac.nz
Without training, rats can detect one of two black arms of a Y-maze that
was previously white during a prior acquisition trial. Although this ability
has featured as a measure of visual recognition memory in studies of retention,
it seems likely that spatial cues determine rats' choices. While all earlier
research has involved male rats only, there is some recent evidence of sex
differences in the behaviour. It is also possible that detection of a change
may be enhanced if, during acquisition, the rats are free to enter and explore
both arms (thereby maximising their spatial characteristics), rather than
merely inspect them through transparent barriers. Effects on responsiveness to
change of the orientation of a Y maze and the nature of acquisition trials were
investigated in hooded rats of both sexes. Only males were affected which
suggested that they depended more on spatial cues than females to detect a
changed arm.