Superior sensitivity for tactile stimuli oriented proximally-distally on the finger: Implications for mixed class 1 and class 2 anisotropies.

Abstract

Inferior performance for obliquely oriented stimuli is often observed on higher level visual and somatosensory tasks and also on tests of low-level visual sensory ability. This study demonstrated an anisotropy of low-level somatosensory performance. Sensitivity to gratings on the finger pad was highest for gratings oriented proximally-distally, intermediate for oblique gratings, and lowest for medial-lateral gratings. This pattern supports a model proposing that detection threshold is determined by the number of neurons tuned to a stimulus (A. Anzai, A. Hearse, Jr., R. D. Freeman, & D. Cai, 1995). A classification of somatosensory and visual anisotropies is proposed in which orientation biases are classified as being attributable to either anisotropic sensory filtering (Class 1) or anisotropic higher level processing (Class 2). It was concluded that a given instance of anisotropic visual or somatosensory performance may stem from low-level sensory factors, high-level factors, or a mixture of the two, depending on the task demands.

Tactile spatial sensitivity and anisotropy

“…Anisotropy has been observed and measured several times on the forearm (Geldard & Sherrick, 1983;B. G. Green, 1982;Vierordt, 1870;Weber, 1834Weber, / 1996 and fingerpad (Essock et al, 1992(Essock et al, , 1997Lechelt, 1988Lechelt, , 1992Stevens & Patterson, 1995;Vierordt, 1870;Weber, 1834Weber, /1996Wheat & Goodwin, 2000) using a variety of different measures of tactile sensitivity. The remaining experiments in this study focused on a systematic investigation of tactile anisotropy.…”

“…These include neural mechanisms such as the size and shape of peripheral receptive fields (termed "sensory circles" by Weber, 1834Weber, /1996Stevens & Patterson, 1995) and orientation-selective neurons in the somatosensory cortex (Essock et al, 1997). Skin ridges have also been proposed as a mechanism Vega-Bermudez & Johnson, 2004;Wheat & Goodwin, 2000): Greater sensitivity at the tip of the finger was observed when grooved contactors were aligned with the dermal ridges rather than perpendicular to the ridges.…”

“…Return to normal performance on the GR/OR task closely paralleled the rate of reinnervation of the primary afferent fibers, as well as the subject's self-report of normal sensory function (Van Boven & Johnson, 1994b). The GR/OR task has also been used as a measure of spatial acuity at a number of different locations on the skin that are known to vary in their density of innervation (Craig, 1999;Craig & Kisner, 1998;Essock, Krebs, & Prather, 1997;Gibson & Craig, 2002;Patel, Essick, & Kelly, 1997;Sathian & Zangaladze, 1996;Van Boven & Johnson, 1994a). In each case, performance on the GR/OR task roughly correlated with changes in density of innervation of the primary afferent fibers.…”

Reference frames and haptic perception of orientation: Body and head tilt effects on the oblique effect

“…In haptics, as was noted by Essock, Krebs, and Prather (1997), the effect of body tilt on the oblique effect has not yet been investigated. However, in a connected field, Van Hof and Lagers-van Haselen (1994) have studied the effect of body tilt on orientation-discrimination by the proprioceptive system.…”

Studying One and Two-Finger Perception of Tactile Directional Cues

“…We also observed that the Vertical direction displays the highest recognition accuracy. This is inline with [1,2] as this direction is generally better recognized as a proximodistal axis.…”