Research reportCapturing the spatial percepts evoked by moving tactile stimuli: a novel approach
Introduction
The complexity of the percepts evoked by simple, point stimuli moved across the skin was demonstrated over 100 years ago by Hall and Donaldson [10]. To minimize response bias and other sources of among- and within-subject variability in measurements of sensory performance, psychophysical procedures have largely ignored the multidimensional and time-varying nature of the percepts. For example, forced-choice procedures are typically employed in studies of direction discrimination [4], [5], [9] and of velocity discrimination [8]. Forced-choice procedures require that the subject assign the complex percept to one of a small number of categories, none of which may accurately describe the perceptual experience. For example, to assess direction discrimination stimuli are usually moved across the test site in two opposing directions, described to the subject prior to testing. After each stimulus, the subject is required to select one of these two options even though the stimulus path perceived might be curved substantially and its average direction different from the stimulus directions by as much as 90°. To maximize performance, the subject selects as his response the stimulus direction for which the difference is <90°.
As a second example, magnitude estimation procedures are typically employed for studies in which subjects judge the length of skin traversed (and the duration or velocity of stimulus motion [6], [7], [8], [13]. Perceived deviations from a linear path are common for a stimulus moving even in a straight line, and it is unclear how this affects the subject's unidimensional response regarding the subjective distance of movement. Few attempts to capture holistic information about the percepts evoked by space- and time-varying stimuli have been reported. Noteworthy in this regard is the work of Langford et al. [11], who asked subjects to draw the path taken by a stylus moved across a linear chord, 12 cm in length, on the volar forearm. These investigators found that the curves were drawn over shorter lengths of skin as the velocity of motion was experimentally varied from 2 to 18 cm/s, and with less irregularity in shape. To our knowledge, the investigators did not pursue this method further to understand tactile perception. Our aim has been to develop computer-assisted approaches for the collection of subjects’ graphical responses (this report) and sophisticated quantitative analyses of the curve data obtained [12]. Based on the ecological and intuitive nature of this approach, we hypothesized that it would be useful in characterizing the altered tactile perception of patients with peripheral or central neural disorders [1]. In order to compare the results with available data obtained with conventional psychophysical procedures, we studied the facial region.
Section snippets
Materials and methods
Four neurologically normal, young adult females (18 to 40 years of age) were recruited to participate in 16 testing sessions each. Five points were marked on the face using a calibrated template to establish an absolute distance, two-dimensional coordinate system (Fig. 1). A digital photograph was taken and morphed to scale the images of the reference points to their actual distances and angles. The mechanical stimulator [2] was securely positioned to deliver constant-velocity brush stimuli
Results
Subjects found the graphical mode of responding intuitive and natural. Upon interviewing after completion of the study, only one subject occasionally referred to the stimuli as ‘up–down/right–left’ suggesting that the precise nature of the stimuli had not been learned. Fig. 2 displays drawings for stimulus movement toward the ear (top panels) and down the face (bottom panels). The substantial diversity in the drawings for the same stimulus conditions likely reflects individual subject factors,
Discussion
We conclude that subjects’ drawings of the path, perceived to have been taken by moving tactile stimuli, contain meaningful information about perception and tactile sensory function. The task is simple, intuitive, and invites application in a clinical setting for which test administration must be rapid and uncomplicated. An obvious limitation is the difficulty in distinguishing the impact on the drawings of changes in sensory discrimination from individual subject factors and biases.
Acknowledgements
This research was funded by the National Institutes of Health Grant Number DE07509 and an unrestricted gift from Unilever Research Port Sunlight. The authors gratefully acknowledge Dr Francis McGlone for support and advice in this developmental effort; Sunil Patel, Dan Davidian and Calvin Wong for assistance with data processing and presentation; and David Fabricant and Ollie Monbureau for automating data collection and digitization. The authors especially thank Professor Ove Franzén for
References (13)
- et al.
Agraphesthesia: a disorder of directional cutaneous kinesthesia or a disorientation in cutaneous space
J. Neurol. Sci.
(1982) Comprehensive clinical evaluation of perioral sensory function
Oral Maxil. Surg. Clin. N. Am.
(1992)Factors affecting direction discrimination of moving tactile stimuli
- et al.
Effects of trauma to the mandibular nerve on human perioral directional sensitivity
Arch. Oral Biol.
(1990) - et al.
Effects of traverse length on human perioral directional sensitivity
J. Neurol. Sci.
(1989) - et al.
Receptor encoding of moving tactile stimuli in humans I. temporal pattern of discharge of individual low-threshold mechanoreceptors
J. Neurosci.
(1995)
Cited by (4)
Quantitative assessment of pleasant touch
2010, Neuroscience and Biobehavioral ReviewsResearch progress of stickiness perception of human body in dressing
2019, Fangzhi Xuebao/Journal of Textile ResearchMixed-model functional ANOVA for studying human tactile perception
2003, Journal of the American Statistical Association