The Influence of Exploration Mode, Orientation, and Configuration on the Haptic Müller-Lyer Illusion

Abstract

We studied the impact of manner of exploration, orientation, spatial position, and configuration on the haptic Müller-Lyer illusion. Blindfolded sighted subjects felt raised-line Müller-Lyer and control stimuli. The stimuli were felt by tracing with the index finger, free exploration, grasping with the index finger and thumb, or by measuring with the use of any two or more fingers. For haptic judgments of extent a sliding tangible ruler was used. The illusion was present in all exploration conditions, with overestimation of the wings-out compared to wings-in stimuli. Tracing with the index finger reduced the magnitude of the illusion. However, tracing and grasping induced an overall underestimation of size. The illusion was greatly attenuated when stimuli were felt with the index fingers of both hands. Illusory misperception was not altered by the position in space of the Müller-Lyer stimuli. No effects of changes in the thickness of the line shaft were found, but there were effects of the length of the wing endings for the smaller, 5.1 cm stimuli. The theoretical and practical implications of the results are discussed.

Attenuating the haptic horizontal—vertical curvature illusion

“…The results are consistent with earlier reports of similar effects by Ballesteros and her colleagues in the study of symmetry (Ballesteros et al, 1998). The use of two hands practically eliminated the haptic Müller-Lyer illusion, even when the stimuli were felt with just two index fingers at the midline (Heller et al, 2005). Bimanual exploration at the midline may prompt more efficient and accurate exploration strategies and, hence, yield improved size estimates.…”

“…The results were somewhat different from those previously reported for the Müller-Lyer illusion (Heller et al, 2005). In that earlier study, the use of two index fingers almost eliminated the Müller-Lyer illusion.…”

“…Egocentric coding with respect to the midline can aid perceptual accuracy and has also been shown to help judgments of the vertical frame of reference (Heller, Calcaterra, Green, & Barnette, 1999). Bimanual exploration also nearly eliminated the Müller-Lyer illusion for touch (Heller et al, 2005). The body is an "object" with a relatively familiar size.…”

“…Ballesteros and her colleagues have shown that haptic symmetry is more readily detected when stimuli are bimanually explored at the midline (Ballesteros, Manga, & Reales, 1997; see also Millar, 2006). Note that Heller et al (2005) found that bimanual exploration at the midline nearly eliminated the Müller-Lyer illusion. Experiment 5 was designed to test the idea that free exploration could explain the possible elimination of the illusion, and subjects felt the stimuli with either their left hands or their right hands at the midline.…”

“…The haptic Müller-Lyer illusion may be diminished with the use of two hands for exploration (see Heller et al, 2005). Perhaps bimanual exploration would have similar effects on the horizontal-vertical illusion.…”