Using a pointing test, perceived location of a target seen in induced motion was evaluated under two display conditions. In one, a fixated, horizontally stationary spot was surrounded by a frame moving back and forth. As the frame moved to each side, its center shifted correspondingly with respect to the subject's objective median plane. In the second display, the surround was constructed so that as it moved back and forth, its center remained in virtual alignment with the objective median plane. Although both conditions produced a substantial induced-motion effect, only the former produced significant shifts in the target's perceived location. Furthermore, similar shifts were also obtained with a stationary, offcenter frame (Experiment 2). This suggests that the changes in perceived location obtained with the first induced-motion display were not derived from the induced motion per se, but, rather, from a frame effect produced when the surround moved to an off-eenter position. Implications for the relationship between perceived motion and position, as well as for two theories of induced motion, are discussed.
PROBLEV A recent study(4) failed to report differences in digit span between braindamaged and non-brain-damaged cases. This may be due t o failure t o take into account side of lesion and intra-hemisphere differences related to difficulties in visual tasks. Although the digit span test is primarily auditory, a number of observations suggest the role of visual imagery, particularly with regard t o digits backward: (1) We have noticed that left hemiplegics with visual problems falter on the backward digits relative to the forward digits.(2) Phenomenologically, the reader is invited to introspect on his own imagery if asked to spell a long word backward, e.g., Washington. (3) One can observe the eye movement of a colleague when presented with forward and backward versions of the task. METHODThe digit span test was administered to 45 left hemiplegics (LIL), 33 right hemiplegics (RHs), and two control groups of normals of high education (CI) (N = 14) and low education (Cz) (N = 24). The groups of hemiplegics were similar in education to C1. The mean age of all groups was in the 60s. The hemiplegic groups were subdivided further on the basis of two or more errors on a visual confrontation task") into those with one or no errors (LHl and RH1) and those with 2 or more errors (LH2 and RHz). RESULTS On Digits Forward, there were no differences among LH1, LHz and GI. All are superior to C2, RHI, RH2 ( p < .05). On Digits Backward, C1 and LH1 are superior to LHZ and Cz, which are superior t o RHI, RHz ( p < .01). For those who scored 6 digits or more on DF, DF-DB yields an average difference score of 3 digits for LH2 and only 2 digits for LH1 and C1. These differences are significant by Mann-Whitney U Test ( p < .01). CONCLUSIONSRHs respond like less educated people on both forward and backward digits. The marked inability of the LH (errors on visual confrontation) to perform on Digits Backward even though they perform normally on Digits Forward is associated with difficulty in visual scanning and possibly eye movements. This view is in accord with that of Hebb(3) and Ewert(2) on the role of visual scanning and memory. I n neuropsychology, it commonly is suggested that verbal factors influence seemingly spatial tasks because of the role of inner language or self-rehearsal. Here we are suggesting a reverse effect. The role of visual scanning in verbal tasks also has clinical importance. It is common to evaluate short term memory by combining Digits Forward and Digits Backward into a composite score, but this practice might obscure important differences. REFERENCES 1. DENNY-BROWN, D. Handbook of Neurological Ezaminatia and Case Recording. Cambridge: 2.3. HEBB, D. 0. 6oncerning imagery. Psychol. Rev., 1968, 75, 466-477. 4. Harvard University Press, 1967 EWERT, H. E e movement during reading and recall. J . Ben. Psychol., 1933, 8, 65-84. STERNE, D. M. The Benton, Porteus and WAIS digit span tests with normals and brain injured subjects.
Two experiments concerning induced movement are reported. The hypothesis was that when outline inducing frames were used, object-relative displacement was modified by two variables, adjacency and apparent speed. Adjacency is directly related to the magnitude of induced movement. Small outline frames are high in adjacency, and so small frames should be powerful generators of induced movement. On the other hand, several investigators have found the speed of the inducing frame to be inversely related to the magnitude of induced movement. It is hypothesized here that this effect of speed was determined by apparent speed (not real speed), and if so, since small objects appeared to move faster than large ones, a small outline frame should be a relatively weak generator of induced movement. In the first experiment, this hypothesis was tested using single inducing frames. In the second experiment, this hypothesis was tested using two inducing frames presented simultaneously. The implications of these experiments were discussed with regard to other theories of induced movement.
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