Evocation and characterization of percepts of apparent motion on the face

Abstract

The percepts evoked by sequential stimulation of sites in close spatial proximity (::=; 2.5 em) on the face were studied. Both method-of-limits and magnitude-estimation procedures were used to identify and characterize alterations in the percepts produced by systematic changes in the temporal and spatial parameters of the sequence. Each site was stimulated by a vertically oriented row of miniature vibrating probes. Apparent motion was consistently perceived when the delay between the onsets of sequentially activated rows (interstimulus onset interval, or ISOl) fell within a relatively narrow range of values, the lower limit of which approximated 5 msec. Both the upper limit and the perceived smoothness and continuity of the motion percepts (goodness of motion) increased with the duration for which each row stimulated the skin over the range evaluated, 15-185 msec. For the successive activation of only two rows, goodness of motion was not influenced by changes in their separation from 0.4 to 2.5 cm. The ISOl values at which magnitude estimates of goodness of motion were highest increased with the duration for which each row stimulated the skin. As such, maximum goodness of motion decreased with increases in the apparent velocity of motion. When the number of sequentially activated rows was increased from two to four or more, the quality of the motion percepts improved. For the successive activation of multiple closely spaced rows, values of ISOI at which numerical estimates of goodness of motion were highest approximated integral fractions of the duration for which each row stimulated the skin. In this situation, the probes rose and fell in a regular, step-locked rhythm to simulate an edge-like or rectangular object moving across the skin. The goodness of motion so attained was relatively independent of the apparent velocity of motion.The movement of a natural object across the skin evokes a rich perceptual experience and one that is acutely sensitive to subtle changes in the physical parameters of stimulation (see, e.g., Essick, Afferica, et al., 1988;Essick, Dolan, Turvey, Kelly, & Whitsel, 1990;Essick, Whitsel, Dolan, & Kelly, 1989). The richness of the percept is hypothesized to reflect, in part, the complexity of the stimulation. For example, a moving brush stimulus not only translates across but also laterally stretches the skin. The two mechanical actions (translation and stretch) generate unique stresses and strains, to which peripheral neural encoding mechanisms are differentially sensitive (Edin, Essick, Trulsson, & Olsson, 1995). To better understand tactile motion perception, we studied the percepts evoked by stimuli that elicit response patterns in the cutaneous mechanoreceptors that are much simpler than those elicited by a natural moving stimulus (see Essick, Rath, Kelly, James, & Murray, 1996). These stimuli were generated by a dense-array tactile stimulator that consisted of a matrix of independently controlled probes, each of which vibrated a small area of skin. With this device, a stimulus tha...

Brain encoding of saltatory velocity through a pulsed pneumotactile array in the lower face

“…In some cases, moving tactile stimulation presented at velocities at the low end of tactile acuity, such as the 5 cm/s presentation here, appear to be processed in cortical networks as discrete stimuli, rather than a constant motion across the skin (Phillips and Johnson, 1985;Trulsson et al, 2000;Wacker et al, 2011;Dépeault et al, 2013). An explanation for this may be that at some velocity threshold, networks of somatosensory neurons switch from processing individual stimuli to processing temporal cues corresponding to consecutive, directional stimulation (Szaniszlo et al, 1998;Tommerdahl et al, 2010). To capture dynamic BOLD activation at the low and high end of this perceptual range, a low but continuous velocity (5 cm/s), a mid-range velocity (25 cm/s), and a relatively high but discernable velocity (65 cm/s) was selected for use in this first study.…”

A broadband tactile array on the fingertip

“…͓For a study involving simultaneous masking, see Weisenberger and Craig ͑1982͒.͔ In addition, both experiments involve discrimination of direction of movement on the array. This topic has been the subject of several previous investigations ͑Essick et Gardner et al, 1992;Gardner and Sklar, 1994;Szaniszlo et al, 1998;Cholewiak and Collins, 2000;Tan et al, 2000͒, although it is not the main focus of the present study.…”