Expanding the tactual field of view

Abstract

Can tactual information be acquired simultaneously by several different fingers? Blind and sighted Ss were asked to scan vertical displays of braille (consisting of either one or two dots) with the index and middle fingers on each hand-using one, two, or four fingers at the same time. Stimuli were recognized most rapidly when the displays were scanned by two fingers on different hands and least rapidly when two fingers on the same hand were used; performance was similar with one finger and with four fingers. The results indicated some parallel perceptual processing of the inputs to the two hands and mutual interference in processing inputs from fingers on the same hand.Braille is read more slowly than print. The reading rates of skilled braille readers have typically been measured at about 60-80 words/min (see Nolan & Kederis, 1969); rates above 100 words/min are rare. Skilled sighted readers. however, commonly read 200-400 words/min, with rates in excess of 1,000 words/min occasionally attained after courses in speed reading.The principal reason for the difference in reading rates evidently derives from a difference in the number of visual and tactual characters that are simultaneously apprehended in a single "glance," rather than from a difference in the speed with which an individual character is processed. Braille readers generally utilize only one finger, usua lIy the index finger, to obtain information from braille text (Fertsch, 1946). The available evidence indicates that this information is processed serially, one character at a time (Foulke, 1964; Nolan & Kederis, 1969). In contrast, skilled sighted readers doubtlessly process printed text in units consisting of many simultaneously perceived letters (Kolers & Katzman, 1966;Reicher, 1969). When printed text is displayed one letter at a time, the reading rate for the visual mode falls to about the same level as for the tactual mode (Troxel, 1967).Braille is embossed in the same left-to-right sequential format as print. But this format might seem less appropriate for braille than for print, tending perhaps to limit the opportunity for sensing more than one character at a time. Although Fertsch (1946) found that many good braille readers employed both index fingers, the best readers usually read the first half of a line with *This report was supported in part by U.S. Office of Education Grant OEG-4-7l-0065 and by National Institute of Mental Health Grant MH-21105 to the first author and by USOE Grant OEG-D-S-0711S5-1S11(032) to the second author. A paper based on this work was presented at the Psychonomic Society convention, St. Louis, November 1971.t Requests for reprints may be sent to J. S. Lappin.Department of Psychology, Vanderbilt University. Nashville. Tennessee 37240. the left index finger and then read the remainder of the line with the right hand. Suppose, however, that braille was embossed with only one word on each line and that a sequence of words appeared in a vertical column down the page: Several fingers might then be used to perceive simul...

Attending to two fingers: Two hands are better than one

“…The present experiments suggest that one reason for Lappin and Foulke's (1973) observation that braille cell perception was better with two fingers on opposite hands is that it is easier to attend to two fingers bilaterally situated. In this regard, it is noteworthy that Tadoma users typically use a single hand (Reed et al, 1982).…”

“…One behavioral measure that suggests that improvement might be seen using fingers from two hands comes from a study of braille reading by Lappin and Foulke (1973). In their study, subjects identified braille cells with one finger, two fingers, or four fingers.…”

Ipsilateral Input Modifies the Primary Somatosensory Cortex Response to Contralateral Skin Flutter

“…Importantly, although some of the published psychophysical findings indicate that concurrent input from mirrorsymmetric sites on the two hands can enhance tactile perceptual performance above that obtained with unilateral stimulation, other studies indicate that tactile input from the two hands can lead to perceptual performance inferior to that observed when the stimulus is applied unilaterally. As examples of the former, (1) Lappin and Foulke (1973) observed that, when a subject scans the pattern using two fingers on opposite hands, Braille cell perception improves over that achieved unilaterally, (2) Craig (1985) reported that a subject's ability to correctly identify a split tactile pattern (dot array) is substantially greater when the two halves of the pattern are presented simultaneously to two fingers on opposite hands (relative to the performance achieved when the two halves are delivered to two fingers, neighboring or nonneighboring, on the same hand), and (3) Essick and Whitsel found that human subjects' accuracy of perceived direction of tactile motion on the hands improves greatly over that obtained with unilateral stimulation when the bilateral stimuli (the sites on the two hands were mirror symmetric) move across the two sites at the same time, in the same direction, and at the same velocity. Essick and Whitsel also reported that, whenever the physical properties of the brushing stimulus applied to one hand differed in some way (e.g., in direction, velocity, relative timing) from those of the stimulus to the opposite hand, the subject's ability to accurately report direction of bilaterally applied stimulus motion declined, often reaching performance levels well below those achieved when each moving stimulus was applied unilaterally (Essick and Whitsel, 1988).…”

Symmetry in haptic and in visual shape perception

“…Blind adults are better than blindfolded sighted people at using the two hands in parallel to recognize shape and orientation (see, e.g., Foulke & Warm, 1967;Warm & Foulke, 1968). Experienced subjects are likely to use the two forefingers in paral1elto scan the sides ofa shape (see, e.g., Lappin & Foulke, 1973) for explicit judgments of symmetry.…”