What do participants expect to experience in the rubber hand illusion? A conceptual replication of Lush (2020)

Abstract

The sense of body ownership (the feeling that the body belongs to the self) is commonly believed to arise through multisensory integration. This is famously shown in the rubber hand illusion (RHI), where touches applied synchronously to a false hand and to the participant’s real hand (which is hidden from view) can induce a sensation of ownership over the fake one. Asynchronous touches weaken the illusion, and are typically used as a control condition. Subjective experience during the illusion is measured using a questionnaire, with some statements designed to capture illusory sensation and others designed as controls. However, recent work by Lush (2020, Collabra: Psychology) claimed that participants may have different levels of expectation for questionnaire items in the synchronous condition compared to the asynchronous condition, and for the illusion-related items compared to the control items. This may mean that the classic RHI questionnaire is poorly controlled for demand characteristics. As such, Lush (2020) suggested that subjective reports in the RHI may reflect compliance or even the generation of experience to meet expectations (‘phenomenological control’), rather than multisensory processes underlying the sense of body ownership. In the current work a conceptual replication of Lush (2020) was performed with an improved experimental design. Participants were presented with a video of the RHI procedure and reported the sensations they would expect to experience, both in open questions and by rating questionnaire items. In keeping with Lush (2020), participants had greater expectations for illusion statements in the synchronous condition compared to the asynchronous condition, and for illusion statements compared to control statements. However, there was also evidence that some expectations may be driven by exposure to the questionnaire items rather than exposure to the illusion procedure. The role of pre-illusion expectations and expectations driven by questionnaire exposure in the RHI require further examination.

Reply to: No specific relationship between hypnotic suggestibility and the rubber hand illusion - Rubber hand effects remain confounded by hypothesis awareness and substantially related to trait phenomenological control

“…However, expectancies are not matched across these conditions. As we reported in the target article 1 and has since been shown elsewhere [3][4][5] , people expect to respond more strongly to the synchronous rather than asynchronous condition. Comparisons between these conditions are therefore confounded by hypothesis awareness (see Corneille & Lush 7 ).…”

“…The second is whether or not the relationships are sufficiently substantial to pose a threat to existing accounts of the RHI. It is important to note that, throughout, Ehrsson et al's commentary fails to appreciate the implications of a critical issue: the asynchronous condition is not a valid control for demand characteristics 1,[3][4][5] The first disagreement regards our reported null relationship between hypnotisability and an RHI difference measure of subjective report (the mean agreement score for three statements describing either referred touch or 'ownership' experience). Ehrsson et al argue that this result contradicts our claims.…”

Sixty years after Orne’s American Psychologist article: A Conceptual Framework for Subjective Experiences Elicited by Demand Characteristics.

“…A crucial assumption underlying the use of these two control methods is that expectancies for illusion and control conditions are matched. However, recent expectancy studies in which participants are merely instructed about RHI procedures show that the assumption is not met: akin to the instruction-based and quasi-control experiments discussed in the previous sections, the pattern of expectancy ratings matches that of typical reports of illusion and control measures (Lush, 2020;replicated by Lush, Seth, et al, 2021;Reader, 2021). The assumption of equal expectancies may not apply to other less commonly employed control conditions; for example, anatomically implausible positioning of a fake hand (Chancel & Ehrsson, 2020) or asynchronous movement (Kalckert & Ehrsson, 2012).…”

Order effects in the rubber hand illusion

“…For contrasts of synchronous and asynchronous stroking to provide support for multisensory integration theories, all relevant factors must be matched across conditions (see Riemer et al, 2019)). However, participant expectancies are not matched across these conditions; contrasts between them are confounded by hypothesis awareness (Lush, 2020;Reader, 2021).…”

“…Similarly, being asked to provide estimates of the position of their own hidden hand before and after the brush stroking procedure may communicate to participants that a change in perceived hand position is anticipated by the experimenter (see . Systematic differences in demand characteristics between presentation order groups would render counterbalancing ineffective (see Reader, 2021).…”