The role of memory and perspective shifts in systematic biases during object location estimation

Our previous research highlighted a systematic bias in a spatial memory task, with participants correctly detecting object movements in the same direction as the perspective shift, whilst misjudging the direction of object movements if those were in the opposite direction to the perspective shift. The aim of the current study was to investigate if the introduction of perspective shifts results in systematic biases in object location estimations. To do so, we asked participants to encode the position of an object in a virtual room and to then estimate the object's sposition following a perspective shift. In addition, by manipulating memory load (perception and memory condition) we investigated if the bias in object position estimates results from systematic distortions introduced in spatial memory. Overall, our results show that participants make systematic errors in estimating object positions in the same direction as the perspective shift. This bias was present in both the memory and the perception condition. We propose that the systematic bias in the same direction as the perspective shift is driven by difficulties in understanding the perspective shifts that may lead participants to use an egocentric representation of object positions as an anchor when estimating the object location following a perspective shift, thereby giving rise to a systematic shift in errors in the same direction as the perspective shift.

Does the Motor System Facilitate Spatial Imagery?

Recent studies have ascertained a link between the motor system and imagery in children. A motor effect on imagery is demonstrated by the influence of stimuli-related movement constraints (i. e., constraints defined by the musculoskeletal system) on mental rotation, or by interference effects due to participants’ own body movements or body postures. This link is usually seen as qualitatively different or stronger in children as opposed to adults. In the present research, we put this interpretation to further scrutiny using a new paradigm: In a motor condition we asked our participants (kindergartners and third-graders) to manually rotate a circular board with a covered picture on it. This condition was compared with a perceptual condition where the board was rotated by an experimenter. Additionally, in a pure imagery condition, children were instructed to merely imagine the rotation of the board. The children’s task was to mark the presumed end position of a salient detail of the respective picture. The children’s performance was clearly the worst in the pure imagery condition. However, contrary to what embodiment theories would suggest, there was no difference in participants’ performance between the active rotation (i. e., motor) and the passive rotation (i. e., perception) condition. Control experiments revealed that this was also the case when, in the perception condition, gaze shifting was controlled for and when the board was rotated mechanically rather than by the experimenter. Our findings indicate that young children depend heavily on external support when imagining physical events. Furthermore, they indicate that motor-assisted imagery is not generally superior to perceptually driven dynamic imagery.

Processing Expectancy Violations during Music Performance and Perception: An ERP Study

Musicians are highly trained motor experts with pronounced associations between musical actions and the corresponding auditory effects. However, the importance of auditory feedback for music performance is controversial, and it is unknown how feedback during music performance is processed. The present study investigated the neural mechanisms underlying the processing of auditory feedback manipulations in pianists. To disentangle effects of action-based and perception-based expectations, we compared feedback manipulations during performance to the mere perception of the same stimulus material. In two experiments, pianists performed bimanually sequences on a piano, while at random positions, the auditory feedback of single notes was manipulated, thereby creating a mismatch between an expected and actually perceived action effect (action condition). In addition, pianists listened to tone sequences containing the same manipulations (perception condition). The manipulations in the perception condition were either task-relevant (Experiment 1) or task-irrelevant (Experiment 2). In action and perception conditions, event-related potentials elicited by manipulated tones showed an early fronto-central negativity around 200 msec, presumably reflecting a feedback ERN/N200, followed by a positive deflection (P3a). The early negativity was more pronounced during the action compared to the perception condition. This shows that during performance, the intention to produce specific auditory effects leads to stronger expectancies than the expectancies built up during music perception.

Face Imagery Is Based on Featural Representations

The effect of imagery on featural and configural face processing was investigated using blurred and scrambled faces. By means of blurring, featural information is reduced; by scrambling a face into its constituent parts configural information is lost. Twenty-four participants learned ten faces together with the sound of a name. In following matching-to-sample tasks participants had to decide whether an auditory presented name belonged to a visually presented scrambled or blurred face in two experimental conditions. In the imagery condition, the name was presented prior to the visual stimulus and participants were required to imagine the corresponding face as clearly and vividly as possible. In the perception condition name and test face were presented simultaneously, thus no facilitation via mental imagery was possible. Analyses of the hit values showed that in the imagery condition scrambled faces were recognized significantly better than blurred faces whereas there was no such effect for the perception condition. The results suggest that mental imagery activates featural representations more than configural representations.

Phase-Locking and Amplitude Modulations of EEG Alpha:

It has been demonstrated in numerous experiments that oscillatory EEG responses in the alpha frequency band (8-12 Hz) increase with memory load during the retention interval in working memory tasks. However, the findings diverge with respect to which measurement of alpha activity is influenced by memory processes. Here, we differentiate between evoked and total alpha activity in order to separate effects of phase-locking and amplitude modulation. We present data from a delayed-matching-to-sample task (S1-S2 paradigm) for which we compared EEG alpha responses between a perception and a memory condition. Increased total alpha activity was found in the retention interval for the memory as compared to the perception condition. Evoked alpha activity, however, did not differentiate between memory and perception conditions but, instead, was increased for the more complex condition of processing non-Kanizsa figures as compared to Kanizsa figures. Thus, our results demonstrate a functional differentiation between evoked and total alpha activity. While alpha phase locking seemed to be influenced mainly by task complexity, alpha amplitude clearly reflected memory demands in our paradigm.

Perceptual Illusions in Imagery

A mental image is in many ways analogous to a percept but it is not completely identical to it. In some respects, visual perception and visual imagery work in different ways. One area which is worth examining with regard to similarities and asymmetries between perception and imagery is the initial phases of visual information processing. The literature includes some references to the equivalence of imagery and perception in optical illusions, but data are contradictory. In our view, a mental image should not be particularly sensitive to variables which are critical in producing an optical illusion, i.e., variables affecting the early phases of information processing and field global effects. Our hypothesis is that an optical illusion will be present in a perception condition but not in an equivalent imagery condition. To test this, we carried out two experiments using the Ebbinghaus illusion and the Ponzo illusion. The results confirmed our hypothesis, demonstrating that there are indeed asymmetries between perception and imagery and that such differences mainly concern specific perceptual processes that differ from those involved in the generation of a mental image.