Perceptual and Motor Skills, 1990, 71, 195-198. O Perceptual and Motor Skills 1990
EFFECT O F ORIENTATION O N VISUAL AND VIBROTACTILE LETTER IDENTIFICATION ' YUTAKA SHIMIZU Industrial Products Research Institute
AND
BARRIE J. FROST Queen 3 University
Summary.-The effect of stimulus orientation of letters presented either visually or vibmtactually was examined to obtain basic information on sensory substitution using the tactile sense. The reaction time (RT) to identify the letters F and R presented in normal or mirror-image form at four orientations each was measured. In addition, conditions of O0 and 270° of head rotation from vertical and arm rotation From the midline axis were employed. Data from 5 trained subjects showed that vibrotactile RTs were always longer than visual RTs. Stimulus rotation away from normal orientation increased visual RTs significantly but not vibrotactile RTs. Visual orientation effect then seemed to be determined by the body-coordinate system but not the vibrotactile orientation. Although further studies are warranted, from the results of this experiment, any convenient and constant stimulus orientation could be used with a wearable vibrotactile display system to exploit passive touch.
Alternate information reception via the tactile modality is necessary for the visually or auditorily impaired person. A vibrotactile display which exploits passive touch is often used as a wearable type of sensory substitution. One of the important problems is to define the spatiotemporal relationship between the origind and the transformed information. This study concerns the effect of orientation of the presented stimulus on the vibrotactile display. Since the study of Shepard and Metzler (1971), the effect of stimulus orientation has been examined as the effects of "mental rotation." Cooper and Shepard (1973) indicated that rotation away from the normal orientation systematically increased visual reaction time (RT) to letter stimuli. The effects of the tactile modality were also examined. Marmor and Zaback (1976) used pattern s t i m d , and Carpenter and Eisenberg (1978) used letter stimuli. Just and Carpenter (1985) reviewed experiments on mental rotation and analyzed the role of the cognitive coordinate system in the spatial ability involved in mental rotation. Furthermore, Heller (1987) indicated superiority of normal orientation in reading both visud and tactual braille. However, the effect of orientation by vibrotactile stimuli using passive touch is not clear. To obtain basic information about designing a vibrotactile display for sensory substitution devices, the following experiments were performed in both visual and vibrotactile modahties.
'Send correspondence to Yutaka Shimizu, Industrial Products Research Institute, 1-1-4, Higashi, Tsukuba, Ibaraki 305, Japan.
196
Y. SHIMIZU & B. J. FROST
A matrix of 7 x 7 solenoid vibrators which were arranged with interspacing of 7 mm between vibrators in both rows and columns, were used for tactile stimuli. The size of the tactile display fitted to the right palm was 42 x 42 mm. A 7 x 7 red LED array was used for visual stimuli. The visual angle of the LED stimulus was about 2.4O. Two capital letters, F and R composed of a 7 x 5 array of elements defined in the middle of the 7 x 7 matrix, were presented at four orientations, 0°, 90°, 180°, and 270°, and measured in a clockwise direction from upright (we denote these conditions V-0 for visual and T-0 for vibrotactile). In addition, conditions of O0 and 90° of head rotation in a counterclockwise direction from vertical were employed (V-270), and 90' of arm rotation from the body midline (T-270) was employed in vibrotactile condition. To produce almost same sensation for the vibrotactile stimuli, activating voltages were adjusted at 12 v for the letter F and at 10.5 v for the letter R, because the defined letter R increased in number by four stimulators more than the letter F. A detailed description of the tactile apparatus was previously published (Shimizu, 1982). Stimuli were presented by a microcomputer system (PDP LSI-11/23). Using the same computer system, RTs were recorded from the rise of stirnulation to the first response of a voice sensor hooked on the subject's throat. The stimulus was offset just at the first voice response from the subject. Subject responded after each presentation whether the stimulus was "F" or "R," and the image was "normal" or "mirror," and the orientation was "OO" or "90°" or "180°" or "270°," respectively. Sixty trials for each condition were measured. Two men and three women, ages 20, 24, 28, 29, and 45 yr. participated.
RESULTS Percentage of correct responses ranged from 75 to 87To in the vibrotactile experiment and 97 to 99% in the visual experiment. Although 12% of the differences were observed for the vibrotactile experiment, no significant dfference was indicated (F,,, = 0.12 to T-0 and F,,, = 0.40 to T-270 among orientations, and F,,, = 0.06 to T-0 and F,,, = 0.11 to T-270 among normal and mirror-images). Then RTs of correct responses were analyzed. Fig. l(a), (b) shows mean RTs as a function of the orientation for the visual experiments, and (c),(d) those of vibrotactile experiments. Visual RTs were always shorter than vibrotactile ones. RTs of visual experiments increased with stimulus rotation away from the normal orientation (the normal orientation means O0 to V-0 and 270° to V-270). Differences among orientations were significant (F,,,= 17.46 to V-0 and F,,, = 14.19 to V-90, p
EFFECT O F ORIENTATION O N VISUAL AND VIBROTACTILE LETTER IDENTIFICATION ' YUTAKA SHIMIZU Industrial Products Research Institute
AND
BARRIE J. FROST Queen 3 University
Summary.-The effect of stimulus orientation of letters presented either visually or vibmtactually was examined to obtain basic information on sensory substitution using the tactile sense. The reaction time (RT) to identify the letters F and R presented in normal or mirror-image form at four orientations each was measured. In addition, conditions of O0 and 270° of head rotation from vertical and arm rotation From the midline axis were employed. Data from 5 trained subjects showed that vibrotactile RTs were always longer than visual RTs. Stimulus rotation away from normal orientation increased visual RTs significantly but not vibrotactile RTs. Visual orientation effect then seemed to be determined by the body-coordinate system but not the vibrotactile orientation. Although further studies are warranted, from the results of this experiment, any convenient and constant stimulus orientation could be used with a wearable vibrotactile display system to exploit passive touch.
Alternate information reception via the tactile modality is necessary for the visually or auditorily impaired person. A vibrotactile display which exploits passive touch is often used as a wearable type of sensory substitution. One of the important problems is to define the spatiotemporal relationship between the origind and the transformed information. This study concerns the effect of orientation of the presented stimulus on the vibrotactile display. Since the study of Shepard and Metzler (1971), the effect of stimulus orientation has been examined as the effects of "mental rotation." Cooper and Shepard (1973) indicated that rotation away from the normal orientation systematically increased visual reaction time (RT) to letter stimuli. The effects of the tactile modality were also examined. Marmor and Zaback (1976) used pattern s t i m d , and Carpenter and Eisenberg (1978) used letter stimuli. Just and Carpenter (1985) reviewed experiments on mental rotation and analyzed the role of the cognitive coordinate system in the spatial ability involved in mental rotation. Furthermore, Heller (1987) indicated superiority of normal orientation in reading both visud and tactual braille. However, the effect of orientation by vibrotactile stimuli using passive touch is not clear. To obtain basic information about designing a vibrotactile display for sensory substitution devices, the following experiments were performed in both visual and vibrotactile modahties.
'Send correspondence to Yutaka Shimizu, Industrial Products Research Institute, 1-1-4, Higashi, Tsukuba, Ibaraki 305, Japan.
196
Y. SHIMIZU & B. J. FROST
A matrix of 7 x 7 solenoid vibrators which were arranged with interspacing of 7 mm between vibrators in both rows and columns, were used for tactile stimuli. The size of the tactile display fitted to the right palm was 42 x 42 mm. A 7 x 7 red LED array was used for visual stimuli. The visual angle of the LED stimulus was about 2.4O. Two capital letters, F and R composed of a 7 x 5 array of elements defined in the middle of the 7 x 7 matrix, were presented at four orientations, 0°, 90°, 180°, and 270°, and measured in a clockwise direction from upright (we denote these conditions V-0 for visual and T-0 for vibrotactile). In addition, conditions of O0 and 90° of head rotation in a counterclockwise direction from vertical were employed (V-270), and 90' of arm rotation from the body midline (T-270) was employed in vibrotactile condition. To produce almost same sensation for the vibrotactile stimuli, activating voltages were adjusted at 12 v for the letter F and at 10.5 v for the letter R, because the defined letter R increased in number by four stimulators more than the letter F. A detailed description of the tactile apparatus was previously published (Shimizu, 1982). Stimuli were presented by a microcomputer system (PDP LSI-11/23). Using the same computer system, RTs were recorded from the rise of stirnulation to the first response of a voice sensor hooked on the subject's throat. The stimulus was offset just at the first voice response from the subject. Subject responded after each presentation whether the stimulus was "F" or "R," and the image was "normal" or "mirror," and the orientation was "OO" or "90°" or "180°" or "270°," respectively. Sixty trials for each condition were measured. Two men and three women, ages 20, 24, 28, 29, and 45 yr. participated.
RESULTS Percentage of correct responses ranged from 75 to 87To in the vibrotactile experiment and 97 to 99% in the visual experiment. Although 12% of the differences were observed for the vibrotactile experiment, no significant dfference was indicated (F,,, = 0.12 to T-0 and F,,, = 0.40 to T-270 among orientations, and F,,, = 0.06 to T-0 and F,,, = 0.11 to T-270 among normal and mirror-images). Then RTs of correct responses were analyzed. Fig. l(a), (b) shows mean RTs as a function of the orientation for the visual experiments, and (c),(d) those of vibrotactile experiments. Visual RTs were always shorter than vibrotactile ones. RTs of visual experiments increased with stimulus rotation away from the normal orientation (the normal orientation means O0 to V-0 and 270° to V-270). Differences among orientations were significant (F,,,= 17.46 to V-0 and F,,, = 14.19 to V-90, p
