The role of instructions and familiar size in absolute judgments of size and distance.

The effects of familiar size and instructions (apparent, objective) on direct reports of size and distance were evaluated. Subjects estimated the size and distance of two different-sized playing cards or two unfamiliar stimuli under either apparent or objective instructions. The stimuli were presented successively at a distance of 5.48 m under reduced-cue conditions. The form of the instructions selectively influenced the effect of familiar size on absolute judgments of size and distance, with apparent instructions minimizing, and objective instructions promoting, familiar-size effects. The ratio of the distance judgments of the first to the second presented stimuli approximated the relative retinal sizes of the two objects under both apparent and objective instructions, while the ratio of size judgments tended to be either influenced by or independent of the object's relative retinal sizes under apparent and objective instructions, respectively. These results are consistent with Gogel's theory of off-size perception and, in particular, with the claim that, in comparison with apparent instructions, objective instructions are more likely to direct observers to base their judgments on cognitive, as opposed to perceptual, sources of spatial information.     

Spatial judgments of exocentric extents in an open-field situation: Familiar versus unfamiliar size

Carlson and Tassone (1971) found that an object of familiar size presented in an outdoor setting and viewed at an appreciable distance is judged to be more distant than an unfamiliar object. Three experiments examined whether object familiarity also affects spatial judgments of exocentric extents presented under conditions comparable to those of Carlson and Tassone’s experiments. The markers of the extents were either familiar or unfamiliar objects. In Experiment 1, subjects reproduced the perceived extents of depth intervals by adjusting a comparison egocentric extent, and in Experiment 2, subjects also compared the relative depths of two equally long extents. In Experiment 3, the two equally long extents were presented in the subjects’ frontoparallel plane, and the subjects reported which of these two extents appeared longer and farther away. The results of these experiments indicate that familiar size does not affect the perceived depths or lengths of exocentric extents viewed under naturalistic conditions.     

Stimulus motion and retrospective time judgments

The effect of stimulus motion on retrospective time judgments was investigated in four experiments. Subjects reproduced the duration of a 32-s interval which was filled by either a stationary or moving visual element presented on a computer monitor. In Experiments 1 and 4, the element moved horizontally back and forth, and in Experiments 2 and 3 it traced a circular pathway. In Experiments 1 and 2, the element moved at speeds of either 5 or 20 cm/s. In Experiment 3, it moved at a constant speed, alternating direction between clockwise and anti-clockwise rotation once every 1, 4, 8 or 16 s. In Experiment 4 the element moved at linear speeds of 1, 2, 4, 8 or 16 cm/s back and forth along a 16 cm horizontal path thereby alternating between left- and rightward motion-directions once every 16, 8, 4, 2 and 1 s, respectively. Temporal reproductions were not systematically influenced by stimulus speed. Rather, the pattern of results indicated a nonmonotonic relationship between remembered duration and the frequency of motion-direction changes; whereas remembered duration was unaffected by either infrequent or very frequent rates of changes, moderate rates of motion-changes lengthens remembered duration. These findings are discussed in relation to the change models of retrospective timing, and the claim that stimulus speed, as distinct from changes in the direction of stimulus motion, is not an important determinant of retrospective timing.     

Spatial range of illusory effects in Müller-Lyer figures

The spatial range of the illusory effects in Müller-Lyer (M-L) figures was examined in three experiments. Experiments 1 and 2 assessed the pattern of bisection errors along the shaft of the standard or double-angle (experiment 1) and the single-angle (experiment 2) M-L figures: Subjects bisected the shaft and the resulting two half-segments of the shaft to produce apparently equal quarters, and then each of the quarters to produce eight equal-appearing segments. The bisection judgments of each segment were referenced to the segment's physical midpoints. The expansion or wings-out and the contraction or wings-in figures yielded similar patterns of bisection errors. For the standard M-L figures, there were significant errors in bisecting each half, and each end-quarter, but not the two central quarters of the shaft. For the single-angle M-L figures, there were significant errors in bisecting the length of the shaft, the half-segment, and the quarter, of the shaft adjacent to the vertex but not the second quarter from the vertex nor in dividing the half of the shaft at the open end of the figure into four equal intervals. Experiment 3 assessed the apparent length of the half-segment of the shaft at the open end of the single-angle figures. Length judgments were unaffected by the vertex at the opposite end of the shaft. Taken together, the results indicate that the length distortions in both the standard and single-angle M-L figures are not uniformly distributed along the shaft but rather are confined mainly to the quarters adjacent to the vertices. The present findings imply that theories of the M-L illusion which assume uniform expansion or contraction of the shafts are incomplete. Received: 15 December 2000 / Accepted: 5 June 2001     

Retrospective time judgements and clock duration

Retrospective time judgements of intervals of 16- and 32-sec. duration were obtained by the method of reproduction. The two intervals were filled either with identical or different stimulus events. Time judgments were influenced by the interval events and by the clock duration of the interval. The results are discussed in relation to various hypotheses of retrospective and prospective timing.     

Illusions and aftereffects of length in the minimal form of the parallel-lines configuration: a reexamination

A number of recent studies have used the graded-series method to measure the illusion and aftereffect distortions of perceived length in the minimal form of the parallel-lines configuration. However, because of some peculiar characteristics of the graded-series method, the aftereffect distortions measured with this method cannot be interpreted unequivocally as reflecting distortions of the perceived length of the test line. On the basis of the results of an experiment that examined the contribution of a possible confound present in the method, it is argued that the method should not be used to measure length aftereffects, and, furthermore, that the results of studies using this method need to be reconsidered.     

Viewing distance and estimates of duration

28 students reproduced the durations of 12- and 18-sec. intervals, which were defined by a moving stimulus on a computer monitor. The monitor was viewed from a distance of either .4 or 2.5 m. Temporal reproductions were significantly greater for the far than for the near distance conditions. Results are considered from the perspective of the change models of timing.     

Framing effects and the reversed Müller-Lyer illusion.

The enclosure hypothesis of the reversed Müller-Lyer illusion was examined in three experiments. In Experiment 1, the ingoing- and outgoing-wings forms of the illusion were measured separately, as a function of the size of the gap between the ends of the shaft and the apices of the wings. In Experiments 2 and 3, the effects of a square frame and of complete and amputated versions of a rectangle on the perceived length of an enclosed horizontal line were examined. For all non-Müller-Lyer illusion figures, an inverted U-shaped function describes the relationship between illusion magnitude and the length of the test line. The peak overestimation of the test line's length was obtained when the ratio of total figure length to test line length was about 3:2. Taken together, the results of the three experiments suggest that the reversed Müller-Lyer illusion can be explained within current theoretical frameworks, such as assimilation theory, without recourse to a special factor of enclosure.     

Influence of the Poggendorff illusion on manual pointing

The results of recent studies indicate that certain visuomotor actions, such as grasping and pointing, are unaffected by visual size illusions. The present study investigated whether the Poggendorff illusion of alignment influences pointing to a target's location. 15 subjects pointed with their unseen hands to the apparent location of the extension of the oblique line onto the target line of a version of the Poggendorff illusion. Analysis indicated the pointing action was influenced by the Poggendorff illusion. The implications of this finding for the claim that different cortical streams of visual processing subserve visuomotor actions and conscious visual perception are discussed.