Biomedical subjects

J Predebon

Publications and source records attributed to J Predebon.

At least 19 recordsLinked to original sources

PubMed2001

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.

Adult↗

PubMed2001

Perceptual strategies to improve skin cancer discriminations in naive observers.

The aim of these experiments was to assess the effect of an educational brochure on the ability of naive observers to discriminate skin cancers from benign lesions, and to investigate possible new strategies to assist observers in performing this task. A two-alternative forced choice paradigm was used to investigate the ability of observers to correctly identify different types of benign and malignant lesions before and after exposure to an educational brochure. The method of pair comparisons was used to assess the ability of observers to discriminate between benign and malignant lesions under different instruction conditions. Subjects were undergraduate students from Sydney University. An educational brochure did not facilitate the ability to correctly identify malignant lesions, and appeared to result in deterioration of performance in the identification of benign lesions. Similarly, observers were unable to discriminate between benign and malignant lesions on the basis of how dangerous they looked. However, judgements of lesions in terms of perceived distinctiveness resulted in relatively accurate discriminations between benign and malignant lesions. These data suggest current skin cancer detection strategies may be ineffective in improving the ability to visually identify benign and malignant lesions. Discriminating between lesions in terms of how distinctive they appear may form the basis of a new and effective strategy for the detection of skin cancer.

Adult↗

PubMed2000

Length illusions in conventional and single-wing Müller-Lyer stimuli.

Warren and Bashford (1977) reported that eliminating one of the wing components from the conventional (i.e., two-wing) Müller-Lyer figures had no appreciable effect on the magnitude of the acute-angle (contraction) illusion but substantially reduced the magnitude of the obtuse-angle (expansion) illusion. In addition, they found that whereas the contractionary effects of the acute-angle components tended to be confined to the region of the shaft adjacent to the angles, the expansionary effects of the obtuse-angle components were more uniformly distributed across the shaft. Since these findings challenge many theories of the Müller-Lyer illusion, the purpose of the present investigation was to evaluate further Warren and Bashford's work with four experiments. Experiments 1 and 2 assessed length illusion magnitudes by requiring subjects to adjust either the length of a plain comparison line to match the length of the Müller-Lyer test figures (Experiment 1) or the length of comparison Müller-Lyer figures to match the length of plain test lines (Experiment 2). Experiments 3 and 4 used a bisection task to assess whether the illusory effects of the angle components are confined mainly to regions of the shaft adjacent to the angles. Consistent with most theories of the Müller-Lyer illusion, eliminating one of the wing components reduced both forms of the Müller-Lyer length illusion to a similar extent. In addition, the acute- and obtuse-angle forms yielded similar patterns of bisection errors, with substantial errors for regions of the shaft adjacent to the angles and negligible errors for regions of the shaft distant from the angles.

Adult↗

PubMed1999

Time judgments as a function of clock duration: effects of temporal paradigm and an attention-demanding nontemporal task.

Participants estimated the duration of one of four intervals (12.5, 25, 37.5, 50 sec.). They performed an attention-demanding nontemporal task (the 'Stroop' task) during the interval's presentation. Half of the participants in each group were told of the time judgment task prior to the interval's presentation (prospective paradigm), and the other half after its presentation (retrospective paradigm). Both prospective and retrospective time judgments substantially underestimated the durations of intervals, and there was no significant effect of temporal paradigm. The results are discussed in relation to the attentional models of timing.

Adult↗

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↗