The Bourdon illusion in haptic space

The bourdon illusion occurs with straight-, right-angle-, and parallel-edge figures

“…In short, the basis of this difference is, for the time being, unclear. Incidentally, it can be noted that the difference is also clearly evident in haptic perception when the fingers are moved across the opposite surfaces of an object with the same frontal profile as Figure 1 (Day, 1990).…”

“…Day (1990) showed that when blindfolded subjects moved thumb and forefinger across the surfaces of objects with the same frontal profiles of the two figures, illusions of bending occurred in the same direction as the visual effects. This suggests that the illusion may be general and that an explanation entirely in terms of visual processes is incomplete.…”

“…However, the size of the illusion in the reverse figure is smaller than that in the standard figure. Since this difference occurred also with right-angle figures (see Experiment 2 below) and in the haptic mode with threedimensional stimulus objects (Day, 1990), it is considered in general terms in the final discussion below. each presentation, the test edges were bent between 5°and 10°about the center of the figure and the direction of initial bentness was also alternated.…”

A brief taxonomy of tactile illusions and demonstrations that can be done in a hardware store

“…In general, they require the production of raised line drawings which are explored in haptic mode, that is via tactile exploration. Day comments that they have been described for a long time [18,66]. Suzuki and Arashida looked at the relative effectiveness of various figures, Müller-Lyer, Oppel-Kundt, Bourdon, Ponzo, Poggendorf, vertical-horizontal, Zöllner, Delboeuf [74], while Heller and Joyner considered the horizontal-vertical effect comparing the behavior blind and sighted people [40].…”

Which way is upright and normal? Haptic perception of letters above head level

“…Both vision and touch are concerned with spatial issues, Indeed, although vision and touch are not identical in their reactions to spatial matters, many assessments of shape made in vision and in touch are the same or tackle similar issues, Novel shape perception and categorization tasks (Garbin, 1988), letter-recognition tasks and subsequent assessments of apparent orientation (Marmor & Zaback, 1976;Oldfield & Phillips, 1983), drawingrecognition tasks (Kennedy, 1993(Kennedy, , 1997, even some illusions, such as the Bourdon (Day, 1990) and MuellerLyer (Rudel & Teuber, 1964) illusions, all have many similar effects when presented in the visual and tactile modalities, Also, practice effects in one modality can be transferred to another (Rudel & Teuber, 1964). Results such as these suggest that, in some respects, haptic and visual modalities provide the observer with spatial information in much the same way (Garbin, 1988;Garbin & Bernstein, 1984;Jones, 1981;Marks, 1978).…”