Biomedical subjects

J Predebon

Publications and source records attributed to J Predebon.

At least 19 recordsLinked to original sources

PubMed1998

Decrement of the Brentano Müller-Lyer illusion as a function of inspection time.

Two experiments are reported in which the decline or decrement in the magnitude of the Brentano Müller-Lyer illusion was measured. Observers made a pre-test judgment and, after a variable intervening time period, a post-test judgment of illusion magnitude. In experiment 1, the intervening time periods were 1, 2, and 3 min during which time the independent groups of observers allocated to each of the three time periods either systematically scanned the Brentano figure (inspection conditions) or waited until the intervening period had elapsed (no-inspection conditions). Experiment 2, which included an additional 5 min intervening time period, evaluated a response-bias explanation for the results of the inspection conditions of experiment 1. Taken together, the findings of the two experiments indicate that sheer inspection of the Brentano figure produces illusion decrement. However, illusion decrement was independent of the duration of the inspection period, with equivalent amounts of decrement occurring across the range of viewing times examined in the two experiments. The pattern of these results suggests that theories of Müller-Lyer decrement must incorporate a factor attributable to, or correlated with, inspection time, whose effect in reducing illusion magnitude is confined mainly to the first 1 or 2 min of active visual inspection of the Brentano illusion figure.

Humans↗

PubMed1996

The role of the angle components in the wings-in and wings-out forms of the Müller-Lyer illusion.

The effect of selective amputations of the angle components in the wings-in (underestimated) and wings-out (overestimated) forms of the Müller-Lyer illusion was examined in two experiments. The stimulus figures consisted of one, two, or four angles. In experiment 1 the method of paired comparisons was used to scale the figures on the psychological continuum of length, and in experiment 2 the method of reproduction was used to obtain quantitative measures of illusion magnitude. There was good agreement between the scaling and the length-reproduction measures of the illusion. The illusory effects in all figures were significant, and the extent of the underestimation and overestimation of the wings-in and wings-out figures, respectively, increased as the number of angles increased. In general, selective amputation of the angle components produced similar patterns of illusory effects in the wings-in and wings-out figures. These findings are discussed with reference to the issue of whether the two forms of the conventional (ie four-angle) Müller-Lyer illusion are similar or distinct illusion types.

Analysis of Variance↗

PubMed1995

Prospective and retrospective time estimates as a function of clock duration.

12 independent groups of 18 subjects each estimated the duration of one of six 'empty' intervals (10, 18, 26, 34, 42, and 50 sec.). Subjects were told of the time task either prior to (prospective paradigm) or after (retrospective paradigm) the presentation of the interval. The results are consistent with Hicks' 1992 finding of an interaction between temporal paradigm and interval duration. Whereas the shorter intervals (< 42 sec.) were estimated accurately in both the retrospective and the prospective paradigms, the longer intervals were estimated rather accurately in the prospective paradigm and underestimated in the retrospective paradigm.

Adolescent↗

PubMed1994

Convergence responses to monocularly viewed objects: implications for distance perception.

In four experiments the role of dark vergence and the implied distance from the familiar-size and suggested-size cues to distance on the convergence response was investigated. A nonius-alignment technique was used to measure the convergence response in total darkness (dark vergence) and the fusion-free convergence response to monocularly viewed objects presented at a distance of 75 cm under otherwise reduced stimulus conditions. Observers also estimated the size and distance of the objects. The results indicated a significant association between individuals' dark-vergence distances and the convergence distances to the objects. Furthermore, the convergence response was influenced by the implied distance from the familiar-size cue but not by the implied distance from size suggestions. Both the familiar-size and the suggested-size cues influenced reports of distance. The implications of these findings for distance perception are discussed with particular reference to the familiar-size cue to distance.

Adult↗

PubMed1994

The familiar-size cue to depth under reduced-cue viewing conditions.

The familiar-size cue to perceived depth was investigated in five experiments. The stimuli were stationary familiar objects viewed monocularly under otherwise completely darkened visual conditions. Perceived depth was measured directly with the method of verbal report and indirectly with the head-motion procedure. Although the familiar-size cue influenced verbal reports of the distances of the objects, it did not determine perceived depth as assessed with the head-motion procedure. These findings support the claim that familiar size is not a major determinant of perceived depth, and that cognitive or nonperceptual factors mediate the effects of familiar size on direct reports of depth and distance. Possible reasons for the failure of familiar size to influence the head-motion-derived measures of perceived depth are discussed with particular emphasis on the role of motion parallax in determining perceptions of depth and relative distance.

Depth Perception↗

PubMed1994

Illusion of length in acute- and obtuse-angle figures.

The apparent expansion and contraction of the length of the arms of an obtuse (160 degrees) and an acute (20 degrees) angle were measured as a function of the relative lengths of the arms. 20 subjects reproduced the apparent length of the fixed-length (50-mm) horizontal lower arm of the angle. The length of the oblique arm was varied from 10 to 90 mm in 20-mm steps. The expansion of the obtuse-angle horizontal arm and the contraction of the acute-angle horizontal arm decreased as a function of the length of the oblique arm. The acute-angle illusion did not reverse from apparent contraction to apparent expansion for the longer oblique arms. These results are relevant to assimilation theories of visual-length distortions; they suggest that the assimilatory processes mediating the angle-length illusion are confined mainly to spatial regions near the vertex of the angle.

Adult↗

PubMed1994

Perceived size of familiar objects and the theory of off-sized perceptions.

In three experiments, I examined the claim (Gogel, 1969; Gogel & Newton, 1969) that familiar objects viewed under reduced stimulus conditions frequently appear to be off-sized (i.e., larger or smaller than normal). In Experiments 1 and 2, I presented images of different familiar objects, one at a time, at distances of 1 and 2 m from the observers. The images were normal-, large-, or small-sized versions of familiar objects, and the observers judged the perceived size of each object relative to its familiar normal size. In Experiment 3, I presented normal-, large-, and small-sized versions of the same familiar object at physical distances of 1 and 2 m. The pattern of size results was similar across the three experiments. In general, normal-sized objects appeared normal-to small-sized at the 1-m distance and small-sized at the 2-m distance; small-sized objects appeared small-sized at the 1-m distance and even smaller at the 2-m distance; and large-sized objects appeared normal- to large-sized at the 1-m distance and normal- to small-sized at the 2-m distance. The distance results of Experiment 3 indicated that familiar size was an effective determinant of reported distance. These results are consistent with Gogel's theory of off-sized perceptions and, more generally, with the claim that familiar size is not an important determinant of perceived size.

Adult↗

PubMed1993

Illusion decrement and transfer of illusion decrement in Müller-Lyer figures.

In the work reported in the literature the reduction or decrement in the magnitude of the Müller-Lyer illusion with continued inspection has been typically investigated with the use of the composite illusion form. Three experiments are reported in which the illusion decrement was separately examined in the underestimated (wings-in) and the overestimated (wings-out) forms of the Müller-Lyer illusion, with particular attention paid to the transfer of illusion decrement between the two forms. Decrement occurred in both forms of the Müller-Lyer illusion, although there was considerable intersubject variability in decrement effects, and nonuniform rates of decrement across the inspection period. In none of the experiments did transfer of illusion decrement between the two forms occur. It is argued that the attentional/differentiation hypothesis of illusion decrement provides a plausible account of the present findings as well as of those found with the composite Müller-Lyer figure.

Adult↗

PubMed1993

The familiar-size cue to distance and stereoscopic depth perception.

The role of the familiar-size cue to distance in stereoscopic depth perception was examined in two experiments. In experiment 1 subjects judged the depth of a binocularly viewed interval, the far point of which was defined by either a familiar or an unfamiliar object, and in experiment 2 subjects adjusted the depth of the interval so that its extent appeared equal to the length of a vertical reference extent positioned on the surface of the object. Although familiar size influenced depth estimates (experiment 1) it did not influence matching judgments (experiment 2). The findings are discussed with reference to the issue of the nature of the familiar-size effects on judgments of stereoscopic depth.

Depth Perception↗

PubMed1992

The influence of object familiarity on magnitude estimates of apparent size.

Three magnitude-estimation experiments were used to determine the exponents of the power function relating size judgments and physical size for two-dimensional familiar and unfamiliar stimuli. The exponent of the power function was used to index the effect of familiar size on perceived size under a variety of conditions, from full-cue to reduced-cue viewing conditions. Although the value of the exponents varied across the three experiments, within each experiment the exponent of the familiar stimulus was not significantly different from that of the unfamiliar stimulus, indicating that familiar size does not influence the rate of growth of perceived size. The results of a fourth experiment excluded a possible explanation of the findings of experiments 1-3 in terms of subjects responding to relative angular size as a consequence of the successive presentation of the different-sized representations of the familiar stimulus. Taken together, the present findings are consistent with the hypothesis that the influence of familiar size on estimates of size mainly reflects the intrusion of nonperceptual processes in spatial responses.

Cues↗

PubMed1992

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.

Adult↗

PubMed1992

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.

Adult↗

PubMed1991

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.

Adult↗

PubMed1990

Relative distance judgments of familiar and unfamiliar objects viewed under representatively natural conditions.

Carlson and Tassone (1971) reported that an object of familiar size viewed at an appreciable distance is perceived to be more distant than an unfamiliar object. Six experiments were designed to examine this effect. The results indicated that the effect is not dependent on Carlson and Tassone's method for assessing perceived relative distance; it occurs at some minimum viewing distance; it is unlikely to be caused by stimulus attributes confounded with the familiar versus unfamiliar size dichotomy; appears to be specific to judgments of the familiar object itself; and it does not occur if the familiar and unfamiliar objects have a common reference target. These findings are discussed with respect to the issue of whether familiar size influences perceived distance as distinct from influencing judgments of distance.

Adult↗

PubMed1990

Illusion decrement and transfer of illusion decrement in obtuse- and acute-angle variants of the Poggendorff illusion.

Illusion-decrement and transfer-of-illusion-decrement procedures were used to examine the contribution of the obtuse- and acute-angle components of the Poggendorff pattern to the standard Poggendorff illusion. In the first four experiments, subjects were required to scan between the oblique lines of the Poggendorff pattern during the inspection phase of the decrement procedure. However, because of a possible confound associated with this procedure, a different decrement technique was used in Experiment 5. The results of Experiment 5 confirm and extend MacKay and Newbigging's (1977) finding that similar amounts of transfer to the standard pattern are obtained from the obtuse- and acute-angle patterns as from the standard pattern itself: In showing that the acute- and obtuse-angle components both contribute to the illusion, these findings question the plausibility of those theories of the Poggendorff illusion which do not assign any significant role to the acute-angle component. Furthermore, the potential confound associated with the decrement procedure of Experiments 1-4 suggests that the results of other studies obtained with similar procedures need to be reevaluated.

Attention↗

PubMed1989

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.

Adult↗

PubMed1988

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.

Attention↗

PubMed1986

The effect of line-figure information on the magnitude of the dot forms of the Poggendorff and Müller-Lyer illusions.

The magnitudes of the dot and line forms of the Poggendorff illusion and the Brentano version of the Müller-Lyer illusion were assessed in two groups of subjects: the informed group was given information about the implied figure configuration in the dot pattern, the uninformed group was not. The informed group produced a significantly greater dot illusion than the uninformed group, and there was no difference between the two groups in the magnitudes of the line illusions. The experiments are discussed in the context of Coren and Porac's proposal that illusion-inducing mechanisms can be divided into structural and cognitive components. The results suggest that about 64% of the magnitude of the Poggendorff illusion and about 54% of the Müller-Lyer illusion can be attributed to the involvement of cognitive factors.

Attention↗