Action Categorization in Rhesus Monkeys: discrimination of grasping from non-grasping manual motor acts

Abstract

The ability to recognize others’ actions is an important aspect of social behavior. While neurophysiological and behavioral research in monkeys has offered a better understanding of how the primate brain processes this type of information, further insight with respect to the neural correlates of action recognition requires tasks that allow recording of brain activity or perturbing brain regions while monkeys simultaneously make behavioral judgements about certain aspects of observed actions. Here we investigated whether rhesus monkeys could actively discriminate videos showing grasping or non-grasping manual motor acts in a two-alternative categorization task. After monkeys became proficient in this task, we tested their ability to generalize to a number of untrained, novel videos depicting grasps or other manual motor acts. Monkeys generalized to a wide range of novel human or conspecific grasping and non-grasping motor acts. They failed, however, for videos showing unfamiliar actions such as a non-biological effector performing a grasp, or a human hand touching an object with the back of the hand. This study shows the feasibility of training monkeys to perform active judgements about certain aspects of observed actions, instrumental for causal investigations into the neural correlates of action recognition.

Categorization learning induced changes in action representations in the macaque STS

“…In line with previous results showing monkeys can learn to discriminate grasping from non-grasping hand actions ( Nelissen and Vanduffel, 2017 ) and left vs right or forward vs backward walking actions ( Vangeneugden et al., 2010 ), with a certain degree of generalization to untrained exemplars, our current findings show monkeys are able to discriminate between grasp, touch and reach actions after training. Although we only trained with a small stimulus set for a limited period of time, both monkeys became proficient in the three-way discrimination task after 30 to 40 training sessions.…”

Anterior Intraparietal Area: A Hub in the Observed Manipulative Action Network

“…The neural machinery underlying observed action processing revealed by the present study also suggests that area AIP should prove an ideal focus for future investigations into the neural basis of the monkeys’ ability to discriminate and categorize hand actions ( Nelissen and Vanduffel 2017 ), as previously investigated for 3D-shapes ( Verhoef et al 2015 ). Interestingly, this function may also benefit from the activity of suppression OMA-selective units that, unlike facilitation units, did not respond during grasping in the dark but did so in the light.…”

MRI Technology for Behavioral and Cognitive Studies in Macaques In Vivo

“…Some primate studies have been carried out on 1.5 T or 3 T scanners (Nelissen and Vanduffel 2017), with a sub-optimal resolution in the range of 2-3 mm. In vivo studies of structural brain imaging at 7 T have been reported in the rhesus macaque (Macaca mulatta), with resolution from 0.3 to 0.5 mm (Zitella et al 2015).…”