Attenuating the haptic horizontal-vertical curvature illusion

Area of Science:

• Psychology
• Neuroscience
• Human Perception

Background:

• The horizontal-vertical illusion (HVI) is a well-documented phenomenon in visual perception.
• Previous research has primarily focused on visual stimuli, with less attention paid to haptic exploration.

Purpose of the Study:

• To investigate the presence and characteristics of the haptic horizontal-vertical illusion.
• To explore the influence of different exploration methods (mon manual, bimanual, free exploration) on the haptic HVI.
• To determine the role of the body midline and movement heuristics in haptic spatial perception.

Main Methods:

• Blindfolded participants traced convex curves with equal horizontal and vertical extents.
• Experiments varied stimulus orientation (frontal plane vs. table surface) and exploration method (single hand, two hands, free exploration at body midline).
• Stimuli were explored using touch (haptics) and, in some conditions, vision.

Main Results:

• A significant horizontal-vertical illusion was observed with haptic curves, where vertical extent was overestimated compared to horizontal extent.
• The haptic HVI was stronger than the visual HVI under certain conditions.
• Bimanual exploration at the body midline, particularly with free exploration, significantly reduced or eliminated the haptic HVI for smaller stimuli.
• The illusion persisted, though weakened, for larger stimuli even with bimanual exploration.
• Exploration in left and right hemispace still elicited the illusion, indicating the benefit stems from midline exploration.

Conclusions:

• The horizontal-vertical illusion is present in haptic perception, similar to visual perception.
• Haptic exploration at the body midline, utilizing the body as a reference, is crucial for accurate spatial judgments and mitigating the HVI.
• Movement-based heuristics and the tactile experience of tracing curve direction may contribute to the haptic HVI.