Academic journal article Attention, Perception and Psychophysics

Inferring the Depth of 3-D Objects from Tactile Spatial Information

Academic journal article Attention, Perception and Psychophysics

Inferring the Depth of 3-D Objects from Tactile Spatial Information

Article excerpt

Published online: 12 March 2015

© The Psychonomic Society, Inc. 2015

Abstract Four psychophysical experiments were conducted to examine the relation between tactile spatial information and the estimated depth of partially touched 3-D objects. Human participants touched unseen, tactile grating patterns with their hand while keeping the hand shape flat. Experiment 1, by means of a production task, showed that the estimated depth of the concave part below the touched grating was well correlated with the separation between the elements of the grating, but not with the overall size of the grating, nor with the local structure of the touched parts. Experiments 2 and 3, by means of a haptic working memory task, showed that the remembered depth of a target surface was biased toward the estimated bottom position of a tactile grating distractor. Experiment 4, by means of a discrimination task, revealed that tactile grating patterns influenced speeded judgments about visual 3-D shapes. These results suggest that the haptic system uses heuristics based on spatial information to infer the depth of an untouched part of a 3-D object.

Keywords Cutaneous input · Somatotopic information · Depth · Haptic working memory · Speeded discrimination

Haptic object recognition involves analyzing tactile spatial and material information through a set of hand movements called exploratory procedures (Lederman & Klatzky, 1987, 2009). Examples of spatial information1 include the layout, shape, and size of touched objects and their parts, whereas examples of material information include the roughness and hardness of touched surfaces (Loomis & Lederman, 1986). For sighted and blindfolded participants, haptic object recognition is easier for familiar 3-D objects than for their 2-D versions such as raised-line drawings (e.g., Klatzky, Loomis, Lederman, Wake, & Fujita, 1993). Lawson and Bracken (2011) found that this was the case even when material information was controlled. Furthermore, these studies reported that recognition performance was better when participants used the hand than when they used only one finger. When participants touch an object with the hand, the haptic system receives much spatial information across a relatively wide area of the skin. How does the haptic system use spatial information in object recognition?

A straightforward idea is that the haptic system uses spatial information to recognize the properties of the touched object parts (e.g., shape, size, and relative location), which may be distinctive enough to identify familiar 3-D objects. Indeed, the haptic system is sensitive to several local properties of objects such as length (Green, 1982), curvature (Goodwin, John, & Marceglia, 1991), and orientation (Frisoli, Solazzi, Reiner, & Bergamasco, 2011; Levy, Bourgeon, & Chapman, 2007). Given that familiar 3-D objects contain more distinctive parts than 2-D patterns do, haptic recognition performance would be better for 3-D objects than for 2-D patterns.

A related but unresolved issue is whether the haptic system uses spatial information to infer or estimate untouched,rather than touched, parts of a 3-D object. For example, when the hand touches a 3-D object with a concave part in real-life situations (Fig. 1a), the outer edges or elements of the concave part can simultaneously stimulate different skin locations separated by a certain distance. At this moment, unless the hand directly touches the bottom of the concave part in a subsequent movement, the haptic system in principle cannot know how deep the concave part is. In vision, an analogous issue has been investigated extensively.2 It is known that the visual system quickly completes partially occluded shapes and edges by using pictorial image cues such as T-junctions (e.g., Rensink & Enns, 1998). In haptics, Kennedy, Gabias, and Nicholls (1991) mentioned that no study had systematically examined whether humans can recognize raised-line drawings that contain T-junctions. …

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