Abstract
Classical neurophysiological studies demonstrated that the monkey brain is equipped with neurons selectively representing the visual shape of the primate hand. Neuroimaging in humans provided data suggesting that a similar representation can be found in humans. Here, we investigated the selectivity of hand representation in humans by means of the visual adaptation technique. Results showed that participants' judgement of human-likeness of a visual probe representing a human hand was specifically reduced by a visual adaptation procedure when using a human hand adaptor but not when using an anthropoid robotic hand or a non-primate animal paw adaptor. Instead, human-likeness of the anthropoid robotic hand was affected by both human and robotic adaptors. No effect was found when using a non-primate animal paw as adaptor or probe. These results support the existence of specific neural mechanisms encoding human hand in the human's visual system.
Highlights
Primates, and in particular humans, are remarkably able to navigate the social environment by relying upon an exceptional ability to process fundamental visual signals about other persons’ face, as facial expression and eye gaze, as well as about other persons’ body, as bodily posture and movement [1,2].The striking ability to deal with these social signals suggested that the primate brain is equipped with neural systems specialized for processing socially relevant information [2]
The adaptor × morphing interaction was significant, F24,1152 = 6.30 p = 0.0001, h2p 1⁄4 0:084; post hoc comparisons showed no differences between the three adaptation conditions from 0 to 15% of morphing ( p > 0.05); from 20 to 35% the score for human hand adaptation was significantly lower with respect to the others two adaptation conditions, and from 40 to 60% the three adaptation conditions were not statistically different ( p > 0.05)
The adaptor × morphing interaction was significant, F24,1152 = 2.863, p = 0.0008, h2p 1⁄4 0:048, with no differences between the three conditions from 0 to 15% of morphing ( p > 0.05); at 20% of morphing, human hand adaptation differed from paw adaptation condition ( p = 0.001), and at 25%, 40%, 45% and 50%, the effect of robot hand adaptation differed from the paw condition
Summary
In particular humans, are remarkably able to navigate the social environment by relying upon an exceptional ability to process fundamental visual signals about other persons’ face, as facial expression and eye gaze, as well as about other persons’ body, as bodily posture and movement [1,2].The striking ability to deal with these social signals suggested that the primate brain is equipped with neural systems specialized for processing socially relevant information [2]. In particular humans, are remarkably able to navigate the social environment by relying upon an exceptional ability to process fundamental visual signals about other persons’ face, as facial expression and eye gaze, as well as about other persons’ body, as bodily posture and movement [1,2]. The most compelling evidence comes from neurophysiological studies revealing single neurons in the monkey inferotemporal cortex selectively discharging royalsocietypublishing.org/journal/rsos R. Classical neurophysiological studies revealed 2 neurons in monkey inferior temporal cortex selectively discharging to the vision of the hand; in particular, these neurons discharged to the presentation of monkey and human hands rather than to the presentation of shapes different from human hands [5,6]
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