How we perceive our own hands: Effects of attention, aging, and sex.

This study investigates whether both the perception of somesthetic sensations arising spontaneously on the hand and their modulation by attention are subject to change with advancing age and sex. Participants aged between 50 and 68 (N = 24), and younger (19-27; N = 24), with an equal sex ratio in each group, described the spontaneous sensations they felt on one of their hands. Two 10-s tests were carried out with participants either seeing their tested hand (gaze towards the visible hand) or not (contralateral gaze, hidden hand). Within the age range covered by our participants, aging had an effect on the spatial distribution of sensations, insofar as the older participants reported feeling more sensations in their palm whereas the younger participants had more sensitive fingers. Age also influenced the number, nature, intensity, and duration of sensations in interaction with gaze and/or sex. The most frequent pattern was a benefit of ipsilateral relative to contralateral gazing in young women. Attentional modulation was seldom observed in men and was absent among older participants.

My heart is in my hands: the interoceptive nature of the spontaneous sensations felt on the hands.

Somatic sensations may arise in the total absence of external stimuli, i.e., spontaneous sensations (SPSs). Because the background of body sensations has been mentioned as a possible contributor to interoceptive functions, such as the perception of the self and the conscious awareness of one's own body, a possible link between SPSs and interoception has been advocated. Yet, no study has provided direct evidence on such a relationship. The aim of the present study was to establish a link between SPSs and interoception. On the basis of the literature, the accuracy of heartbeat perception was taken as an index of general interoception across different bodily modalities. It was found that individuals with good heartbeat perception experienced more numerous and more intense SPSs. Furthermore, taken along with other individual characteristics, heartbeat perception accuracy predicted the perceived intensity of SPSs, their spatial extent, their variety, as well as confidence in their spatial characteristics. However, we also provide evidence that good vs. poor heartbeat perception is not just a matter of degree. We conclude that interoception definitely contributes to the perception of SPSs.

Interacting effects of vision and attention in perceiving spontaneous sensations arising on the hands.

Visual input and attention enhance tactile perception. But do they influence the perception of spontaneous sensations (SPS) arising in the absence of any external stimulus? We have investigated this by requiring subject to focus attention on each hand while orienting overtly toward it (convergent focusing) or away (divergent focusing) and to subsequently describe the properties of the SPS they felt. Subjects performed this task under free viewing conditions or while blindfolded. Enhanced perception of SPS was found under convergent focusing and also under free viewing conditions. However, the effects of focusing were different whether visual input was available or not. When visual input was available, SPS were enhanced in the fingers but suppressed in the palm, suggesting that enhancement and suppression operated to refine perception of SPS. When visual input was unavailable, only enhancement was observed, even in areas of the hand where suppressing effects were found under free viewing conditions. These interacting effects between vision and attention were observed exclusively in the left hand. A control experiment failed to evidence whether looking at different parts of the hand modulates SPS. We suggest that vision facilitates perception and, when interacting with attention, it enables better perception by promoting suppression of SPS arising in areas of lower sensitivity that may interfere with processing in more sensitive zones. The results are discussed with respect to mechanisms lateralized in the right cerebral hemisphere, and a role of SPS in the maintenance of a conscious image of the body is suggested.