Boris Crassini

Approaches to Studying of Australian and Overseas Chinese University Students

Abstract This article takes up the question of whether the approaches to study adopted by Australian students and overseas Chinese students differ. Participants in the study consisted of 202 first‐year Australian students and 248 first‐year overseas Chinese students drawn from two Australian universities. The students were tested using the Approaches to Studying Inventory (ASI). The data obtained from the two groups were subjected to factor analysis (with orthogonal rotation). For Australian students, a four‐factor structure in studying approaches, which accounted for 55.6% of the total variance, was obtained. The factors were: Meaning Orientation; Non‐Academic Orientation; Anxious‐Rigid Orientation; and Goal Orientation. For the overseas Chinese students, a four‐factor structure in studying approaches which accounted for 52.8% of the total variance was obtained. The factors were: Anxious‐Surface Orientation; Self‐Motivated Reflective Orientation; Efficiency Orientation; and Comprehension Orientation. Alt...

The influence of optic expansion rates when judging the relative time to contact of familiar objects

Previous research has shown that size-dependent errors in time-to-contact (TTC) judgments can be attenuated when approaching objects are familiar to the observer and have a known size. We describe two experiments that show that the effect of size on relative TTC judgments can be modeled on observers reliance on the instantaneous optic expansion rates of the approaching objects. This reliance on optic expansion rates occurred independently of object familiarity and when the actual TTC of the approaching objects was relatively brief or relatively long. However, observers sensitivity to differences in TTC was improved for familiar objects when TTC was large. These results are consistent with other research showing that optic expansion rate is a critical variable for judging TTC.

The effects of familiar size and object trajectories on time-to-contact judgements

Many interceptive actions involve interactions with objects that are familiar to the observer and have known sizes. Two experiments investigated how known size influences observers’ perception of time-to-contact (Tc). Participants made Tc judgements of objects that were either ambiguously sized, standard-size in identity/familiarity, or off-size in identity/familiarity, and simulated as approaching on linear trajectories (Experiment 1), or linear versus parabolic trajectories (Experiment 2). In Experiment 1, Tc judgements were influenced by the size of the object in the three object identity/familiarity conditions; the greatest size effect occurred in the off-size condition compared to the ambiguous size and standard-size conditions. The results of Experiment 2 replicated these results and found that size effects were not reduced with displays simulating parabolic trajectories, that is, displays simulating ecologically valid free-falling objects. Taken together, the finding that Tc judgements are influenced by object identity/familiarity does not provide support for the tau hypothesis, nor the hypothesis that Tc judgements are based solely on optic expansion rates. However, the results do provide support for the proposition that Tc judgements are based on a combination of rate of retinal image expansion and object identity/familiarity information, the latter information requiring observers to have prior experience with, or knowledge about, the objects.

Spatial summation in young and elderly observers

We measured detection thresholds for targets over a range of sizes at both photopic and scotopic luminance levels in young and elderly observers, and used these data to estimate spatial summation areas 10 degrees in the retinal periphery. There were differences in detection thresholds between the young and old groups at photopic and scotopic luminances, but no differences in spatial summation areas at either background luminance level.

The roles of static depth information and object-image relative motion in perception of heading.

In a series of 6 experiments, two hypotheses were tested: that nominal heading perception is determined by the relative motion of images of objects positioned at different depths (R. F. Wang & J. E. Cutting, 1999) and that static depth information contributes to this determination. By manipulating static depth information while holding retinal-image motion constant during simulated self-movement, the authors found that static depth information played a role in determining perceived heading. Some support was also found for the involvement of R. F. Wang and J. E. Cuttings (1999) categories of object-image relative motion in determining perceived heading. However, results suggested an unexpected functional dominance of information about heading relative to apparently near objects.

Spatial-frequency-contingent color aftereffects: Adaptation with one-dimensional stimuli

The McCollough effect was shown to be spatial-frequency selective by Lovegrove and Over (1972) after adaptation with vertical colored square-wave gratings separated by 1 octave. Adaptation with slide-presented red and green vertical square-wave gratings separated by 1 octave failed to produce contingent color aftereffects (CAEs).However, when each of these gratings was adapted alone, strong CAEs were produced. Adaptation with vertical colored sine-wave gratings separated by 1 octave also failed to produce CAEs, but strong effects were produced by adaptation with each grating alone. By varying the spatial frequency of the test sine wave, CAEs were found to be tuned for spatial frequency at 2.85 octaves after adaptation of 4 cycles per degree (cpd) and at 2.30 octaves after adaptation of 8 cpd. Adaptation of both vertical and horizontal sine-wave gratings produced strong CAEs, with bandwidths ranging from 1.96 to 2.90 octaves and with lower adapting contrast producing weaker CAEs. These results indicate that the McCollough effect is more broadly tuned for spatial frequency than are simple adaptation effects.

Barber-Pole Illusions and Plaids: The Influence of Aperture Shape on Motion Perception

The barber-pole illusion and its influence on plaid perception were investigated in two experiments to test the following expectations: (i) apertures which bias the perception of grating motion in directions consistent with plaid direction will facilitate plaid perception, and (ii) apertures which bias the perception of grating motion in directions inconsistent with plaid direction will disrupt plaid perception. In experiment 1 the barber-pole illusion was measured as a function of grating orientation (20°, 45°, and 70°, clockwise and counterclockwise from horizontal), and aperture shape (vertical, horizontal; at each of three elongations). Barber-pole illusions reported with 45° gratings increased with increased aperture elongation. However, this was not found with 20° and 70° gratings; these were almost always reported as moving in a direction parallel to the side of the aperture with which the gratings formed angles approaching 90°. In experiment 2 this dependence of barber-pole illusions on the relative orientation between gratings and apertures was also evident with 45° gratings in oblique apertures; only oblique directions of grating motion were reported. The influence of the same apertures on the separate contrast thresholds required for initial plaid coherence and initial plaid decomposition was measured. In experiments 1 and 2, coherence thresholds were unaffected by apertures, contrary to expectation (i). However, in both experiments expectation (ii) was confirmed; decomposition thresholds decreased in apertures which biased perceived direction of gratings towards vertical (plaid direction), and increased in apertures which biased grating motion away from vertical. Adaptation of plaid mechanisms during measurement of decomposition thresholds was proposed to explain the discrepancy between coherence and decomposition data. Taken together, the results were interpreted as reflecting interactions between mechanisms mediating the barber-pole illusion and mechanisms mediating plaid perception.

Spatial-frequency-contingent color aftereffects: Adaptation with two-dimensional stimulus patterns

The spatial-frequency theory of vision has been supported by adaptation studies using checkerboards in which contingent color aftereffects (CAEs) were produced at fundamental frequencies oriented at 45dg to the edges. A replication of this study failed to produce CAEs at the orientation of either the edges or the fundamentals. Using a computer-generated display, no CAEs were produced by adaptation of a square or an oblique checkerboard. But when one type of checkerboard (4 cpd) was adapted alone, CAEs were produced on the adapted checkerboard and on sine-wave gratings aligned with the fundamental and third harmonics of the checkerboard spectrum. Adaptation of a coarser checkerboard (0.80 cpd) produced CAEs aligned with both the edges and the harmonic frequencies. With checkerboards of both frequencies, CAEs were also found on the other type of checkerboard that had not been adapted. This observation raises problems for any edge-detector theory of vision, because there was no adaptation to edges. It was concluded that spatial-frequency mechanisms are operating at both low- and high-spatial frequencies and that an edge mechanism is operative at lower frequencies. The implications of these results are assessed for other theories of spatial vision.

Anomalous Spiral Aftereffects: A New Twist to the Perception of Rotating Spirals

Stationary spirals viewed after inspecting rotating sectored disks appear to rotate and to expand or contract radially, even though the rotating disks contain no perceptible components of radial motion. Moreover, the relative directions of illusory rotation and radial motion observed in these instances are ‘impossible’ under the stimulus constraints normally imposed by the geometry of a spiral under rotation: the stationary spirals appeared to expand/contract in directions opposite to those normally observed under conditions of actual spiral rotation, and under conditions of illusory spiral rotation in classical spiral aftereffects.

The influence of object-image velocity change on perceived heading in minimal environments.

When human observers move forward and rotate their eyes, a complex pattern of light flows across the retina. This pattern is referred to asretinal flow. A model has been proposed to explain how humans perceive their direction of self-movement (orheading) from (1) static depth, (2) direction of image motion, and (3) whether image velocity undergoes acceleration or deceleration (Wang & Cutting, 1999). However, findings from past research in which sparse or minimalist stimuli were used have suggested that not all of the information to which participants are sensitive is captured within the scope of this model. In particular it has been suggested that themagnitude orsize of image velocity change may be of significance beyond simply whether image velocity could be categorized as speeding up (i.e., accelerating) or slowing down (i.e., decelerating). In two experiments, the influence of this factor on heading judgments under minimal conditions was investigated. Evidence was found in support of the idea that the rate of image velocity change can influence judgments of the direction of self-movement in minimalist conditions.