Academic journal article Attention, Perception and Psychophysics

The Projected Hand Illusion: Component Structure in a Community Sample and Association with Demographics, Cognition, and Psychotic-Like Experiences

Academic journal article Attention, Perception and Psychophysics

The Projected Hand Illusion: Component Structure in a Community Sample and Association with Demographics, Cognition, and Psychotic-Like Experiences

Article excerpt

Published online: 14 August 2014

© The Psychonomic Society, Inc. 2014

Abstract The projected hand illusion (PHI) is a variant of the rubber hand illusion (RHI), and both are commonly used to study mechanisms of self-perception. A questionnaire was developed by Longo et al. (2008) to measure qualitative changes in the RHI. Such psychometric analyses have not yet been conducted on the questionnaire for the PHI. The present study is an attempt to validate minor modifications of the questionnaire of Longo et al. to assess the PHI in a community sample (n = 48) and to determine the association with selected demographic (age, sex, years of education), cognitive (Digit Span), and clinical (psychotic-like experiences) variables. Principal components analysis on the questionnaire data extracted four components: Embodiment of "Other" Hand, Disembodiment of Own Hand, Deafference, and Agency-in both synchronous and asynchronous PHI conditions. Questions assessing "Embodiment" and "Agency" loaded onto orthogonal components. Greater illusion ratings were positively associated with being female, being younger, and having higher scores on psychotic-like experiences. There was no association with cognitive performance. Overall, this study confirmed that self-perception as measured with PHI is a multicomponent construct, similar in many respects to the RHI. The main difference lies in the separation of Embodiment and Agency into separate constructs, and this likely reflects the fact that the "live" image of the PHI presents a more realistic picture of the hand and of the stroking movements of the experimenter compared with the RHI.

Keywords Rubber hand illusion . Embodiment . Agency . Self-perception . Principal components analysis . Psychotic-like experiences

Introduction

In the past 16 years, the Rubber Hand Illusion (RHI, Botvinick & Cohen, 1998) has received much interest as an experimental paradigm for investigating mechanisms of selfperception, which may be defined as the perception of one's self, including thoughts and actions, as residing within the physical body (Arzy et al., 2006a, b). In the illusion, a fake hand is placed in front of a participant and stroked with a paintbrush while the participant's real hand, out of their vision, is stroked simultaneously (synchronous condition). In many healthy individuals, this produces a striking illusory sensation of displacement of the felt location of one's own hand, sensation of touch through the rubber hand, and 'embodiment' (or "ownership") of the rubber hand which refers to the sensation that the rubber hand belongs to one's body (that the rubber hand is one's own hand; e.g., Heed et al., 2011; Longo et al., 2008; Newport, Pearce, & Preston, 2010). Embodiment of the rubber hand arises from a combination of processes, including the correlation and reconciliation of conflicting temporal and spatial information from the visual and tactile systems, and from 'visual capture', or increased weighting of visual over tactile and proprioceptive stimuli (Holmes, Snijders, & Spence, 2006; Pavani, Spence, & Driver, 2000; Rossetti, Desmurget, & Prablanc, 1995; Spence, Pavani, & Driver, 2000; Tipper et al., 1998). The RHI thus provides valuable insight into how multiple sensory modalities are integrated to contribute to self-perception.

The illusion can be abolished or diminished by introducing a temporal delay between brush strokes on each hand (asynchronous condition; Botvinick & Cohen, 1998). Given that embodiment of a body part requires synchronous input between sensory modalities, such as touch and vision, introduction of such a delay between brush strokes often is sufficient to prevent the occurrence, or reduce the strength, of the illusion. This "asynchronous condition" often is used as a comparison condition to the synchronous condition (Botvinick & Cohen, 1998; Shimada, Fukuda, & Hiraki, 2009).

Qualitative changes in perception on the RHI are typically rated using a questionnaire administered at the end of each condition. …

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