The Horizontal–Vertical Curvature Illusion in Touch Is Present in Three-Dimensional Objects and Raised Lines (original) (raw)

2013, The American Journal of Psychology

AI-generated Abstract

The horizontal-vertical curvature illusion, prevalent in both vision and touch, leads to the overestimation of vertical extents compared to horizontal ones. This study investigates whether utilizing three-dimensional (3-D) objects and free exploration methods can reduce or eliminate this illusion, revealing that it remains strong even in the presence of such stimuli. Results indicate that the illusion is influenced by the configuration and mode of exploration, with particular emphasis on the role of radial and tangential motions in the perception of these dimensions.

The visual perception of length along intrinsically curved surfaces

Perception & Psychophysics, 2004

The ability of observers to perceive three-dimensional (3-D) distances or lengths along intrinsically curved surfaces was investigated in three experiments. Three physically curved surfaces were used: convex and/or concave hemispheres (Experiments 1 and 3) and a hyperbolic paraboloid (Experiment 2). The first two experiments employed a visual length-matching task, but in the final experiment the observers estimated the surface lengths motorically by varying the separation between their two index fingers. In general, the observers' judgments of surface length in both tasks (perceptual vs. motoric matching) were very precise but were not necessarily accurate. Large individual differences (overestimation, underestimation, etc.) in the perception of length occurred. There were also significant effects of viewing distance, type of surface, and orientation of the spatial intervals on the observers' judgments of surface length. The individual differences and failures of perceptual constancy that were obtained indicate that there is no single relationship between physical and perceived distances on 3-D surfaces that is consistent across observers.

Touching trajectories: the relation between speed and curvature in exploring shape

Studies in motor psychophysics have documented that the tangential velocity of movement decreases with increasing curvature of the path being followed. Views on the origin of this relation range from higher order motion planning processes such as trajectory selection according to a principle of minimisation of mean squared rate of change of acceleration (jerk) to lower level motor constraints, for instance sinusoidal constraint on joint motion. We have examined finger-scanning movements in which eight subjects traced repeatedly round various raised outline shapes. We were interested to see whether velocity would be related to curvature from the outset, suggesting low level sensorimotor constraints, or whether the relation would emerge with experience, as a result of increased trajectory planning. We found evidence of a relation between speed and curvature from the outset, in support of lower level, rather than trajectory planning, constraints.

DOI:10.1068/p2964 Raised line drawings are spontaneously explored with a single finger

2000

Abstract. In this study we examine the strategies used by blindfolded subjects asked to freely explore raised line drawings and identify what is depicted in them. We were particularly interested in how often a single finger is spontaneously used because in several studies subjects are forced to use only one fingertip and the extent to which this restriction may depress haptic perception is unclear. The results suggest that despite a variety of strategies, people `naturally ' use single fingertips sufficiently often to allow confidence in conclusions that are based on studies imposing this restriction. 1

Raised line drawings are spontaneously explored with a single finger

Perception, 2000

In this study we examine the strategies used by blindfolded subjects asked to freely explore raised line drawings and identify what is depicted in them. We were particularly interested in how often a single finger is spontaneously used because in several studies subjects are forced to use only one fingertip and the extent to which this restriction may depress haptic perception is unclear. The results suggest that despite a variety of strategies, people`naturally' use single fingertips sufficiently often to allow confidence in conclusions that are based on studies imposing this restriction.

The perception of doubly curved surfaces from intersecting contours

Perception & Psychophysics, 1987

The perception of a three-dimensional (3-D) surface shape can be inferred from a 2-D image of two intersecting curves. Three experiments are reported in which we examined a possible method for determining the surface shape as a function of the geometry at the point of intersection. The method involves a two-step process in which the tangents to the two curves determine a skewed Cartesian coordinate system. The angle of the quadrant containing two arcs, the double arc quadrant (DAQ), is then examined. Experiment 1 showed that the surface is perceived as hyperbolic when the DAQ is acute and as locally convex when the DAQ is obtuse. Experiments 2 and 3 showed that even when the DAQ is 90°, the underlying 3-D shape may be unambiguously judged as either hyperbolic or locally convex. It is suggested that the viewer may use an extrapolation process in order to differentiate between these potentially ambiguous stimulus configurations.

A Thickness Illusion: Horizontal Is Perceived as Thicker than Vertical

Vision

We report two psychophysical experiments that investigate a visual illusion that is considered common knowledge among type designers, but has never been studied scientifically. Specifically, the thickness of a horizontal line is overestimated in relation to that of a vertical line. Experiment 1 confirmed the existence of the illusion. In Experiment 2, we replicated the effect and showed that the illusion is closely related to the vertical-horizontal illusion, in which the length of a vertical line is overestimated in comparison to a horizontal one. Both the overestimation of thickness and length is larger when the stimulus is surrounded by a horizontally elongated frame, as opposed to a vertically elongated frame. We discuss potential explanations for the thickness illusion and its relation to the vertical-horizontal illusion.

Perception of Moving Lines: Interactions Between Local Perpendicular Signals and 2D Motion Signals

Vision Research, 1997

An oblique line translating vertically behind a horizontal rectangular aperture is perceived as moving in the horizontal direction, i.e., in the line-ending's direction. When a feature is added on the line, and thus provides a vertical unambiguous motion signal, the line's perceived direction is still horizontal. In parallel, the feature appears to slide obliquely along the line (Wallach, 1935). We first show that this finding which we call "the sliding effect" is robust and easy to replicate for different orientations of the rectangular aperture (up to about 20 deg from vertical). This effect also occurs with an invisible circular aperture. In this case, using an adjustment task observers have great difficulty extracting the actual direction of the feature (a gap or a dot on the line). Instead, a systematic bias towards the direction of "sliding" is observed. This misperception of the feature's velocity is markedly reduced or even suppressed when the circular aperture is outlined or when a visible circle is drawn around this invisible aperture. The line's perceived direction is always roughly orthogonal to the line's orientation regardless of the presence of a visible circular outline. This latter result is important because it shows that the feature on the line does not disambiguate the perpendicular signals extracted along the contour, even in conditions where this feature's motion is almost correctly perceived. Altogether, these results suggest that line-endings are not used by the visual system in the same way as a feature on the line when it comes to determining the line's perceived direction.

Visual and haptic matching of perceived orientations of lines

2003

In this study we investigated the perception and production of line orientations in a vertical plane. Previous studies have shown that systematic errors are made when participants have to match oblique orientations visually and haptically. Differences in the setup for visual and haptic matching did not allow for a quantitative comparison of the errors. To investigate whether matching errors are the same for different modalities, we asked participants to match a visually presented orientation visually, haptically with visual feedback, and haptically without visual feedback. The matching errors were the same in all three matching conditions. Horizontal and vertical orientations were matched correctly, but systematic errors were made for the oblique orientations. The errors depended on the viewing position from which the stimuli were seen, and on the distance of the stimulus from the observer.

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