Misalignment effects in 3-D versions of Poggendorff displays

Strong misalignment effects are found in three-dimensional (3-D) versions of Poggendorff displays viewed binocularly. The components of the standard 2-D Poggendorff figure—the parallels and the oblique segments—were presented in 3-D depth as a flat rectangular object with occluding edges and an oblique line situated behind the object. Three experiments investigated the misalignment effects under three different observation instructions: Subjects were told to look at the oblique (Experiment 1), at the rectangle (Experiment 2), or at the background (Experiment 3). Experiments 1 and 2 examined the effects on judgments of alignment of varying the distance in depth that separates the oblique from the rectangle. Experiment 3 examined the effects of varying the distance between the fixated background and the 3-D Poggendorff figure. Both standard and reversed misalignment effects were obtained. When the viewing condition produces crossed disparity for the oblique, perceived misalignment occurs in the usual Poggendorff direction, but it is reversed with uncrossed disparity. Moreover, the amount of misalignment is related to the amount of disparity, and it can be much stronger than is usual in the 2-D versions of the Poggendorff. The misalignment effects can be explained by binocular integration to produce a single cyclopean image.     

Book reviews

Darwin's Dangerous Idea, Daniel C. Dennett, 1995. London, Penguin. 587 pp., hbk £25, ISBN: 0–713–99090–2

Verificationism: Its History and Prospects, C. J. Misak, 1995. London and New York, Routledge. xviii + 254 pp. ISBN: 0–415–12597–9(hbk); 0–415–12598–7(pbk)

Abductive Inference: Computation, Philosophy, Technology, John R. Josephson & Susan G. Josephson (Eds), 1994. Cambridge, Cambridge University Press 306 pp.

Physics and Metaphysics. Theories of Space and Time, Jennifer Trusted, 1994. London, Routledge 210 pp.     

The morphological asymmetry of the hemispheres and cerebral dominance for speech: A possible relationship

The asymmetry of the posterior Sylvian branches of the middle cerebral artery was examined on the carotid angiograms of 59 patients in whom the lateralization of speech representation was known from sodium amobarbital (Amytal) studies. The usual asymmetry of these vessels was found to be present in the group of patients with left-hemisphere speech representation but significantly reduced in patients with atypical cerebral dominance for speech. A model of the inheritance of handedness and cerebral dominance is extended to take account of these results.     

Regional cerebral blood flow response to recognition memory versus semantic classification tasks

Two randomly assigned groups, N = 7 each, of neurologically normal patients were composed. One group, RM, had regional cerebral blood flow measurements during a recognition memory probe test; the other group, SC, had rCBF measurements during a semantic classification task, using the same stimulus and response features as the RM task. Thus, the groups differed only in the cognitive instruction they were executing. The RM group showed a significantly lower change from resting baseline to activation, in mean left hemisphere initial slope index, than did the SC group. The RM group, but not the SC group, showed a significant inverse correlation between occipital flow and accuracy of memory performance as indicated by d′. Correlations between age and hemispheric initial slope index, and between homologous left and right hemisphere sites, were also described. The results are considered to support an anatomical basis for the distinction between episodic and semantic memory and to suggest that occipital flow may diminish with accurate memory performance because of an upstream demand of blood in the medial temporal lobes.