An objective neural signature of rapid perspective taking

Abstract

The frequency-tagging approach has generally been confined to study low-level sensory processes and always found related activation over the occipital region. Here for the first time, we investigated with it, high-level socio-cognitive functions, i.e. the processing of what other people are looking at which is referred to as level 1 visual perspective taking (VPT). Sixteen participants were presented with visual scenes alternating at 2.5 Hz which were depicting a person and an object in a room, while recording electrophysiological brain activity. The person orientation and object position changed at every stimulus but the person in the room always faced the object, except on every fifth stimulus. We found responses in the electroencephalography (EEG) spectrum exactly at the frequency corresponding to the presentation of the scenes where the person could not see the object, i.e. 0.5 Hz. While the 2.5 Hz stimulation rate response focused on typical medial occipital sites, the specific 0.5 Hz response was found mainly over a centro-parietal region. Besides a robust group effect, these responses were significant and quantifiable for most individual participants. Overall, these observations reveal a clear measure of level 1-VPT representation, highlighting the potential of EEG frequency-tagging to capture high-level socio-cognitive functions in the brain.

Keywords: EEG; fast periodic visual stimulation; frequency tagging; theory of mind; visual perspective taking.

Fig. 1.

Stimuli and paradigm. (A) Examples of stimuli used in the experiment. (B) Experimental paradigm (see also Video S1). Different stimuli appear at each stimulation cycle (no repetition within a stimulation sequence), with a randomly changed size to prevent pixel-based adaptation. Stimuli are presented by sinusoidal contrast modulation at the rate of 2.5 Hz (i.e. stimuli reached full contrast after 0.2 s). The embedded periodic response of interest was 0.5 Hz. Note that the side of the object location and the direction faced by the person could vary randomly at every cycle, and only the specific relationship between the two changed at 0.5 Hz. A full stimulation sequence lasted 94 s (84 s stimulation plus 5 s of fade-in and fade-out; see Supplementary Movie S1).

Fig. 2.

Responses at the frequencies of interest. (A) Scalp topography (SNR) of the grand average of the periodic and nonperiodic trials of the sum of the 5th first harmonic (excluding 2.5 Hz) with the selected ROIs for further analysis. (B) SNR spectrum over the centro-parietal ROI and the frontal ROI of the periodic trials (left) and the nonperiodic trials (right).

Fig. 3.

Illustration of individual participants’ SNR response to changes of perspective consistency over one electrode belonging to one ROI. The spectrum is centered at the response of the summed of the five significant harmonics, surrounded by the summed of the neighboring bins, which indicate noise levels (for visibility only the five neighboring bins on each side are shown).