Several studies have reported that, when subjects have to judge the laterality of rotated hand drawings, their judgment is automatically influenced by the biomechanical constraints of the upper limbs. The prominent account for this effect is that, in order to perform the task, subjects mentally rotate their upper limbs toward the position of the displayed stimulus in a way that is consistent with the biomechanical constraints underlying the actual movement. However, the effect of such biomechanical constraints was also found in the responses of motor-impaired individuals performing the hand laterality judgment (HLJ) task, which seems at odds with the “motor imagery” account for this effect. In this study, we further explored the source of the biomechanical constraint effect by assessing the ability of an individual (DC) with a congenital absence of upper limbs to judge the laterality of rotated hand or foot drawings. We found that DC was as accurate and fast as control participants in judging the laterality of both hand and foot drawings, without any disadvantage for hands when compared to feet. Furthermore, DC's response latencies (RLs) for hand drawings were influenced by the biomechanical constraints of hand movements in the same way as control participants' RLs. These results suggest that the effect of biomechanical constraints in the HLJ task is not strictly dependent on “motor imagery” and can arise from the visual processing of body parts being sensitive to such constraints.

In this paper, we report the case of RS, a brain-damaged patient presenting with a disproportionate conceptual impairment for fruit and vegetables in comparison to animals and artefacts. We argue that such a finer-grained category-specific deficit than the living/nonliving dichotomy provides a source of critical evidence for assessing current alternative theories of conceptual organisation in the brain. The case study was designed to evaluate distinct expectations derived from the categorical and the knowledge-specific accounts for category-specific semantic deficits. In particular, the integrity of object-colour knowledge has been assessed in order to determine whether the patient's deficit for fruit and vegetables was associated with a deficit for that kind of knowledge, which has been claimed to be highly diagnostic for fruit and vegetables. The results showed that the patient's pattern of performance is consistent with theories assuming a topographical category-like organisation of conceptual knowledge in the brain.

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Motor theories of action comprehension claim that comprehending the meaning of an action performed by a conspecific relies on the perceiver's own motor representation of the same action. According to this view, whether an action belongs to the motor repertoire of the perceiver should impact the ease by which this action is comprehended. We tested this prediction by assessing the ability of an individual (D.C.) born without upper limbs to comprehend actions involving hands (e.g., throwing) or other body parts (e.g., jumping). The tests used a range of different visual stimuli differing in the kind of information provided. The results showed that D.C. was as accurate and fast as control participants in comprehending natural video and photographic presentations of both manual and nonmanual actions, as well as pantomimes. However, he was selectively impaired at identifying point-light animations of manual actions. This impairment was not due to a difficulty in processing kinematic information per se. D.C. was indeed as accurate as control participants in two additional tests requiring a fine-grained analysis of an actor's arm or whole-body movements. These results challenge motor theories of action comprehension by showing that the visual analysis of body shape and motion provides sufficient input for comprehending observed actions. However, when body shape information is sparsely available, motor involvement becomes critical to interpret observed actions. We suggest that, with natural human movement stimuli, motor representations contribute to action comprehension each time visual information is incomplete or ambiguous.