How imagery changes self-motion perception

Abstract

Imagery and perception are thought to be tightly linked, however, little is known about the interaction between imagery and the vestibular sense, in particular, self-motion perception. In this study, the observers were seated in the dark on a motorized chair that could rotate either to the right or to the left. Prior to the physical rotation, observers were asked to imagine themselves rotating leftward or rightward. We found that if the direction of imagined rotation was different to the physical rotation of the chair (incongruent trials), the velocity of the chair needed to be higher for observers to experience themselves rotating relative to when the imagined and the physical rotation matched (on congruent trials). Accordingly, the vividness of imagined rotations was reduced on incongruent relative to congruent trials. Notably, we found that similar effects of imagery were found at the earliest stages of vestibular processing, namely, the onset of the vestibular-ocular reflex was modulated by the congruency between physical and imagined rotations. Together, the results demonstrate that mental imagery influences self-motion perception by exerting top-down influences over the earliest vestibular response and subsequent perceptual decision-making.

Keywords: decision making; imagery; self motion perception; vestibular.

Fig. 1

Experimental set-up and protocol. (A) The subject is seated in the dark on a vibration-free motorized rotating chair that can move rightward (light gray arrow) and leftward (dark gray arrow). Eye movements are recorded using EOG at all times and the perception of rotations is indicated by a two button press hand held device. (B) A recording of a single trial, which begins with the lights going off followed by an audio cue to inform the subject of the direction of the imagined rotation. The chair then starts rotating after 6–8 s with an exponential increase in velocity (note the chair velocity trace represents the true velocity of the chair). The subject indicates the direction of the chair rotation with a button press, following which the chair comes to a gentle halt. At the end of the trial, the lights are switched on and the subject is asked to rate the vividness of the imagery on a scale of 0–3. The onset of nystagmus is indicated by a top pointing arrow.

Fig. 2

Effect of different imagery conditions on vestibular–ocular reflex and perceptual thresholds. (A) The oculomotor threshold was significantly reduced if the imagined rotation was in the same direction as the chair rotation (i.e. congruent) compared to the condition in which no imagery was present (i.e. neutral). In contrast, if the imagined rotation was in the opposite direction to the chair rotation (incongruent) then the oculomotor threshold was increased. (B) A statistically significant increase in perceptual threshold was found between the incongruent and incongruent conditions, which was also present for the oculomotor thresholds (A).

Fig. 3

Plot illustrating the absence of correlation between the imagery congruency effect on perceptual measures (i.e. incongruent – congruent scores) and the imagery congruency effect on oculomotor measures.

Fig. 4

Effects of attentional cuing upon vestibular perceptual thresholds. As can be observed, there was no difference in perceptual thresholds for either the congruent or incongruent conditions when compared to each other or the condition with no attentional cue (i.e. neutral condition).