Time-to-Collision (TTC) judgements with offsize objects show that Tau needs to be intergrated with familiar size to explain TTC performance

Observers judged TTC with computer-generated displays simulating an approaching object in three familiar-size conditions:(i) Real-size (smaller, larger objects depicted as tennis, soccer balls respectively).(ii) Off-size (smaller, larger objects depicted as soccer, tennis balls respectively).(iii) Ambiguous-size (smaller, larger objects depicted as texture-less black balls of different size).Displays simulated objects approaching observers&iacute; viewpoint from 24.96 m, and disappearing at 5.76 m. Manipulation of approach velocities (4.8-19.2 msec-1) produced viewing times from 1.0 to 4.0 sec, and delays between object disappearance and tau-based TTC ranging from 0.3 to 1.2 sec. Motion characteristics of smaller and larger objects in the three familiar-size conditions simulated those of approaching real-sized tennis and soccer balls respectively; that is, for each approach velocity, tau&sbquo;-based TTC was the same across the three conditions for smaller and larger objects.Results showed that, consistent with the proposition of tau-determined TTC, TTC estimates in the real-size condition were uninfluenced by object size. This is contrary to previous reports that TTC for larger objects is underestimated relative to TTC for smaller objects. However, such size-dependent TTC differences were found in the ambiguous-size condition, with even larger differences in the off-size condition; TTCs for the &euml;larger&iacute; tennis ball were much less than TTCs to the &euml;smaller&iacute; soccer ball compared to corresponding TTCs in the ambiguous-size condition. These results are problematic for the proposition that tau solely determines TTC. We discuss the role of perceptual learning in resolving this problem.<br /

Investigations of perception and imagery using CAEs: The role of experimental design and psychophysical method

Orientation-contingent color aftereffects (CAEs) were measured using 174 observers ran-domly allocated to one of eight experimental conditions formed by the factorial combination of three two-level factors. These were experimental design (pretest and posttest measures taken vs. posttest measures taken alone), psychophysical method (forced-choice vs. magnitude estimation), and inspection procedure (inspection of real contours vs. inspection of imagined contours). In addition to color responses, written introspective reports of the strategies used in providing color responses were obtained. As a basis for the rejection of observers using inappropriate strategies, reported strategies were coded as appropriate or inappropriate. An analysis of the color reports of all observers was performed, as well as two analyses of the color reports of only those observers identified as using appropriate response strategies. In all cases, the results showed that CAEs were reported after inspection of real contours irrespective of the experimental design or psychophysical method used. There were no significant CAEs reported in any conditions that involved the imagination of contours. A separate analysis of the relationship between observers' response strategies, the coding of these strategies, and observers' actual color reports revealed some problems concerning the use of such introspective techniques. The implications of these findings are discussed in terms of theoretical assumptions about the nature of imagery and perception

Auditory-visual integration in neonates: A signal detection analysis

The ability of neonates to integrate auditory and visual information into a single percept was investigated using a signal detection methodology. Thirty-two infants (mean age = 4.6 days) were presented with an auditory stimulus (the word "baby" spoken once, or repeated four times) from either directly ahead (catch trials), or to the infant's side (signal trials); lateral displacements of 45° left or right, and 90° left or right were used. A video recording of neonates' oculomotor behavior during the experimental session was made for later independent scoring by two judges. The methodology enabled separate performance indices of sensitivity and response bias to be calculated for both ipsilateral and contralateral eye turns. Subsequent analyses of these indices showed that while neonates displayed a significant bias toward not responding (p < .001), ipsilateral eye turns occurred more frequently than expected by chance (p < .001). The frequency of eye movements was not influenced by either the duration of the auditory stimulus, the degree of lateral displacement, or whether the sound was presented from the left or right of the midline. The methodological implications of these results are discussed in relation to previous investigations of auditory-visual coordination

Making ambiguous displays unambiguous: The influence of real colors and colored aftereffects on perceptual alternation

The relationship between orientation-contingent colored aftereffects (CAEs) and perceptual alternation of ambiguous displays was investigated in three experiments. In all experiments, the ambiguous test display consisted of vertical and horizontal contours that either could be perceived as separate surfaces (the diamond organization) or could be combined to form upright and inverted Us (the rectangles organization). In Experiments 1 and 2, observers inspected the test display when it was achromatic, when it was colored in a manner consistent with the appearance of CAEs, and when it was colored in a non-CAE manner. In Experiment 3, the test display was inspected monocularly before and after monocular color-orientation adaptation. The achromatic viewing conditions of Experiments 1 and 2, both monocular preadaptation achromatic viewing conditions of Experiment 3, and the postadaptation achromatic viewing condition involving the nonadaptation eye in Experiment 3 produced essentially the same results: reports of approximately equal duration for the diamond and rectangles organizations and steady rates ofperceptual alternation. The non-CAE color conditions of Experiment 2 produced a similar pattern of results. However, the color condition of Experiment 1 (i.e., simulated CAEs), and the postadaptation condition involving the adaptation eye in Experiment 3 produced a decrement in the perceptual alternation rate, with the diamond organization being reported almost exclusively. These results indicate that ambiguous displays can be made unambiguous by altering the appearance of the displays either through the addition of appropriate colors or by exposing observers to appropriate adaptation conditions. These results are consistent with stimulus-bound explanations of both CAEs and perceptual alternation