Academic journal article Attention, Perception and Psychophysics

Visual and Visually Mediated Haptic Illusions with Titchener's [Perpendicular]

Academic journal article Attention, Perception and Psychophysics

Visual and Visually Mediated Haptic Illusions with Titchener's [Perpendicular]

Article excerpt

Published online: 7 March 2014

© Psychonomic Society, Inc. 2014

Published online: 7 March 2014 # Psychonomic Society, Inc. 2014

Abstract For a replication and expansion of a previous experiment of mine, 14 newly recruited participants provided haptic and verbal estimates of the lengths of the two lines that make up Titchener's [perpendicular]. The stimulus was presented at two different orientations (frontoparallel vs. horizontal) and rotated in steps of 45 deg around 2π. Haptically, the divided line of the [perpendicular] was generally underestimated, especially at a horizontal orientation. Verbal judgments also differed according to presentation condition and to which line was the target, with the overestimation of the undivided line ranging between 6.2 % and 15.3 %. The results are discussed with reference to the two-visual-systems theory of perception and action, neuroscientific accounts, and also recent historical developments (the use of handheld touchscreens, in particular), because the previously reported "haptic induction effect" (the scaling of haptic responses to the divided line of the [perpendicular], depending on the length of the undivided one) did not replicate.

Keywords Visual illusion . Haptic signaling . Perception and action . Neural interactions . Historical developments

Titchener's [perpendicular] (Titchener, 1901) is a famous illusion figure that has been widely used in vision research (e.g., Charras & Lupiáñez, 2009, 2010; Finger & Spelt, 1947; Mamassian & de Montalembert, 2010; McBride, Risser, & Slotnick, 1987; Wolfe, Maloney,&Tam, 2005), and also in the field of haptic- tactile perception (e.g., Heller, Bracket, Salik, Scroggs, & Green, 2003; Tedford & Tudor, 1969). Both the visual and haptic illusions typically consist in perceiving the undivided line of the [perpendicular] to be longer than the divided one when both are of the same length (but see Taylor, 2001, for exceptional individuals; Heller et al., 2003, for a possible inversion of the haptic-tactile illusion with solid objects; and Hamburger & Hansen, 2010, for individual differences in amounts of the visual illusion). Since the seminal work of Künnapas (1955), the visual illusion is known mainly to reside in the bisection of the divided line by the undivided one, rather than in the orientation of the figure (horizontal, vertical, or oblique), which exerts only a minor influence (Landwehr, 2009). Because of this confound, many researchers prefer to use Sanford's L (Sanford, 1898) instead of Titchener's [perpendicular] when studying orientation effects (e.g., Avery & Day, 1969; Pearce &Taylor, 1962; Thompson&Schiffman, 1974). The presence of the T-junction in the [perpendicular] figure also affects (or may even be essential for) the haptic-tactile illusion (Day & Avery, 1970), although, in this perceptual system, the illusion mainly seems to be based on the temporal demands of specific arm movements that have to be carried out to explore the stimulus (Armstrong & Marks, 1999; Heller, Calcaterra, Burson, & Green, 1997; Wong, 1977; see Marchetti & Lederman, 1983, for a refutation ofWong's suggestion that inertial factors might be involved, and McFarland & Soechting, 2007, for a cautionary note concerning order effects). Hence, although the visual and the haptic-tactile [perpendicular] illusions describe similar phenomena, the bases of the effects observed seem to be quite different (Gentaz & Hatwell, 2004; Lederman & Jones, 2011).

Renewed interest in visual and haptic illusions arose when Aglioti, DeSouza, and Goodale (1995) demonstrated that observers may err on a visual, judgmental task, yet correctly grasp a target object that is part of the same, illusion-inducing figure. This surprising dissociation, which has often (although not always) been replicated, was taken as evidence for the existence of two visual systems, one subserving motor coordination and another mediating categorization (Milner & Goodale, 2006, 2008; see Schenk, Franz, & Bruno, 2011; Westwood & Goodale, 2011, for recent reviews; and de Haan & Cowey, 2011; Kravitz, Saleem, Baker, & Mishkin, 2011, for the current neuroscientific status of the theory). …

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