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PubMed1975

The role of perceptual cues in the trapezoid oscillatory illusion.

The present experiment was designed to test the hypothesis that binocular disparity functions as a veridical cue, and linear perspective as a nonveridical cue in the perception of a rotating trapezoid. Three trapezoids with proportionately increasing slope were viewed by 10 subjects through viewing screens designed to control the availability of binocular disparity. Monocular and binocular viewing conditions were employed. The dependent variable, proportion of perceived oscillation, was analyzed by a factorial analysis of variance and appropriate post hoc tests. The obtained data indicate that increasing the availability of binocular disparity by increasing viewing screen width favors veridical rotation perception. When the binocular depth cue was attenuated by decreasing viewing screen width, the observer relied on linear perspective, and non-veridical oscillation perception was favored. As linear perspective was increased by increasing trapezoid slope, perceived oscillation increased both monocularly and binocularly. However, for any level of linear perspective, monocular viewing invariabily produced more oscillation than binocular viewing, indicating that monocular depth cues (movement parallax and interposition) were not as effective at neutralizing the illusory perspective effect as the binocular disparity cue.

Adolescent↗
PubMed1995

Feeling the parts: a developmental study of separable perception with tactile dimensions.

A tetrad classification task was used to determine perceptual sensitivity to the tactile dimensions of texture, hardness, and shape in 5- and 11-year-old children who classified objects by touch, unaided by vision. Both age groups reliably used separate dimensions to group the objects. Both age-related and individual differences in dimensional salience were observed. Five-year-olds predominantly grouped objects that were identical in hardness; 11-year-olds most often grouped objects identical in hardness or shape. Overall (integral) similarity was not used reliably by any participant. Results support the differential-sensitivity view of cognitive development and are consistent with Garner's (1970) distinction between integral and separable stimulus structure, but they do not support the hypothesized developmental trend from integral to separable perception.

Age Factors↗
PubMed2006

Perceived orientation of complex shape reflects graded part decomposition.

Although the orientation of line segments and simple shapes is a well-studied area of vision, little is known about geometric factors that influence perceived orientation of complex multipart shapes. The study of these factors is of interest because it allows for an insight into the basic problem of how local geometric attributes are integrated perceptually into a global shape representation. We examined the perceived orientation of two-part shapes using an adjustment method and a 2AFC task. In particular, we investigated the influence of the perceptual salience, or distinctiveness, of a part--as defined by the turning angles at its boundaries--and its area relative to the main "base" part. In contrast to previous results on simple shapes, our results exhibited large and systematic deviations of perceived orientation from the principal axis of the shape. For shapes with sharp part boundaries, perceived global orientation deviated maximally from the principal axis and was approximated by the axis of the main base part of the shape. With weakening part boundaries, the perceived orientation gradually approached the principal axis of the entire shape, reflecting that both parts were taken into account in estimating orientation. The results are consistent with a differentially weighted principal-axis computation in which the attached part is given systematically lower weighting with increasing turning angles at the part boundaries. They thus allow a quantitative characterization of part salience in terms of part independence: Turning angles at a part's boundaries determine the extent to which its influence is perceptually separable from the rest of the shape. We suggest that Robust Statistics may provide a useful framework for quantifying the influence of part segmentation on visual estimation.

Adult↗
PubMed1983

Influence of line context on power function parameters.

Stimuli in experiments in which line-lengths are judged are typically single lines. In studies in which area and volume are judged, the stimuli are typically more complex. An experiment with 22 college undergraduates investigated whether differences in context (single lines versus lines in depicted boxes) influenced the exponent or scaling factor of the power function of length judgments. The scaling factor of the power function was significantly affected by context, but the exponent of the power function was not.

Discrimination Learning↗