Tactile confusions of the fingers and toes.

Abstract

Recent research has shown systematic patterns of confusions between digits of the hands and feet. The present study addressed whether such confusions arise from early somatosensory maps or higher level body representations. As the glabrous and hairy skin of the hands and feet have distinct representations in somatosensory cortex, an effect arising from early somatotopic maps may show distinct patterns on each skin surface. In contrast, if the effect arises from higher level body representations which represent the digits as volumetric units, similar patterns should be apparent regardless of which side of the digit is touched. We obtained confusion matrices showing the pattern of mislocalization on the glabrous and hairy skin surfaces of the toes (Experiment 1) and fingers (Experiment 2). Our results replicated the characteristic pattern of mislocalizations found on the glabrous skin reported in previous studies. Critically, these effects were highly similar on the hairy skin surface of both the toes and fingers. Despite the pattern of mislocalizations being highly stereotyped across participants, there were consistent individual differences in the pattern of confusions across the two skin surfaces. These results suggest that mislocalizations occur at the level of individual digits, consistent with their resulting from higher level body representations. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

A Systematic Comparison of Perceptual Performance in Softness Discrimination with Different Fingers

“…Furthermore, our assumptions are also in line with previous findings in volume perception (Zhang et al, 2018;Zhang et al, 2019), spatial acuity (Ducan & Boynton, 2007;Manser-Smith et al, 2018;Sathian & Zangaladze,1996;Schweizer et al, 2000;Vega-Bermudez & Johnson, 2001) and two-point discrimination (Louis et al, 1984). The previous findings in tactile sensitivity are not completely uniform concerning differences between the individual fingers, but the general pattern shows a decreasing sensitivity from the large index and middle fingers to the smallest little finger.…”

“…Differences in grip and press strength show that the middle and index fingers are stronger than the ring and little fingers, whereas the little finger is the worst (Li, Latash, & Zatsiorsky, 1998 ; MacDermid et al, 2004 ; Talsania & Kozin, 1998 ; Quaine, Vigouroux, & Martin, 2003 ). Additionally, results from Louis et al ( 1984 ), Manser-Smith et al ( 2018 ), and Schweizer et al ( 2000 ) indicate a declining spatial acuity from index and middle fingers to the ring finger and to the little finger. The results are also in line with Zhang et al ( 2018 , 2019 ), who found a better performance for index and middle fingers as compared to the ring and small fingers in volume perception.…”

“…It has also been suggested that fingers differ in the sensory ability to perceive pressure, spatial acuity, and in their two-point discrimination threshold (Dellon, Mourey, & Dellon, 1992 ; Louis et al, 1984 ; Manser-Smith et al, 2018 ; Sathian & Zangaladze, 1996 ; Schweizer et al, 2000 ; Vega-Bermudez & Johnson, 2001 ; Weinstein, 1968 ). However, previous results are somewhat heterogeneous.…”

“…However, previous results are somewhat heterogeneous. In some studies investigating point localization and two-point discrimination, a better performance for thumb, index, and middle finger as compared to ring and small finger in the glabrous skin was found (Manser-Smith et al, 2018 ). The little finger seems to have the worst localization threshold (Louis et al, 1984 ; Schweizer et al, 2000 ).…”

A common representation of fingers and toes

“…One line of evidence for this comes from Gerstmann syndrome (Gerstmann, 1939), in which some patients show specific deficits in identifying digits, whether fingers or toes (Mayer et al, 1999;Tucha, Steup, Smely, & Lange, 1997). Another line of evidence comes from recent studies of tactile localisation in healthy adults, which have identified distinct patterns of confusions between the fingers and toes, but with some similarities in mislocalisations (Cicmil, Meyer, & Stein, 2016; Manser-Smith, Tamè, & Longo, 2018;Schweizer, Braun, Fromm, Wilms, & Birbaumer, 2001;Tamè, Wühle, Petri, Pavani, & Braun, 2017). For example, digits of both the hands and feet are more frequently mislocalised to neighbouring than distant digits, however not equally to each neighbouring digit, but more often in the direction of the central digits of the hand or foot (Cicmil et al, 2016;Manser-Smith et al, 2018).…”