No evidence that monkeys attribute mental states to animated shapes in the Heider–Simmel videos

Abstract

Human Theory of Mind (ToM) is so automatic and pervasive that we spontaneously attribute mental states to animated abstract shapes, as evidenced by the classic Heider–Simmel findings. The extent to which this represents a fundamental characteristic of primate social cognition is debated. Prior research suggests that monkeys spontaneously predict behavior and attribute basic goals to conspecifics, but it remains unclear whether, like humans, they spontaneously ascribe mental states to animated shapes. Here, we address this question by analyzing rhesus monkeys’ viewing patterns of the classic Heider–Simmel animations. We hypothesized that if rhesus monkeys also spontaneously attribute mental states to animated shapes, then, like humans, they would have the longest fixation durations for theory of mind animations, medium duration fixation for goal-directed animations, and shortest fixations for animations with random motion. In contrast, if attributing mental states to animations is specific to humans and perhaps other apes, then we predict no differences in looking time across animation categories. Unlike humans, monkeys did not fixate longer on ToM videos. Critically, monkeys’ viewing patterns did not correlate with humans’ viewing patterns or intentionality ratings from previously published research. The only major difference in viewing patterns between animation categories tracked differences in low-level visual motion. Thus, monkeys do not view the classic Heider–Simmel animations like humans do and we found no evidence that they spontaneously attribute mental states to animated shapes.

Gaze patterns and brain activations in humans and marmosets in the Frith-Happé theory-of-mind animation task

“…In contrast to Klein et al (2009), however, Schafroth et al (2021 did not find longer fixation duration for Frith-Happé's ToM animations in macaque monkeys. Here, we confirmed the results of Klein et al (2009) in humans, whereas marmosets, like macaques (Schafroth et al, 2021), did not show any significant difference between fixation durations in the two types of animations.…”

“…By conducting mixed analyses of variance (ANOVA), with factors of species (Human vs Marmoset) and condition (ToM vs Random animation videos), we found a significant interaction between species and condition (F(1,22)=7.67, p=.01, ηp 2 =.258). Here we observed longer fixation durations for ToM animation videos (M=317.2 ms) as compared to Random videos (M=269.0 ms) for humans (p =.029) but not for marmosets (258.3 ms vs 270.5 ms, p=.81).This finding confirms that humans fixate longer in the ToM condition (Klein et al, 2009) whereas marmosets, like macaques (Schafroth et al, 2021), do not show this effect.…”

“…We then went further than the previous studies in humans (Klein et al, 2009) and macaques (Schafroth et al, 2021) and investigated the proportion of time subjects looked at each of the two triangles, the protagonists of the animations. While there was no difference in the proportion of time subjects looked at the large red and the small blue triangles during Random animations, both humans and marmosets spent significantly more time looking at the large red triangle during ToM compared with Random animations.…”

Social prediction modulates activity of macaque superior temporal cortex

“…On the other hand, midSTS interactions with the visual system in macaques might reflect stronger dependencies of TOMrelated computations on visuo-social information. This constraint might explain why macaques did not distinguish between socially and randomly interacting abstract shape as previously observed (48) despite their abilities for face pareidolia (49). These between-species differences might reflect greater specialization of TPJ in humans that may have occurred in association with the expansion and reorganization ( 16) of the temporal cortex in the hominid evolution.…”

Seeing social: A neural signature for conscious perception of social interactions

“…Whether such animations are seen as social depends largely on the movement patterns of the agents (Castelli et al, 2000;Gao et al, 2009). This phenomenon appears to transcend age (Gordon & Roemmele, 2014;Rochat et al, 1997) and culture (Barrett et al, 2005), although interestingly, is not found in monkeys (Schafroth et al, 2021). Individuals with certain neurological or psychiatric conditionsmost notably autism-are less likely to perceive social interactions in these animations (Abell et al, 2000;Fong et al, 2017;Klin, 2000;Langdon et al, 2020) and show commensurately lower activity in typical social processing regions of the brain (Castelli, 2002;Herrington et al, 2007;Kana et al, 2009Kana et al, , 2015.…”