A Live Experience of Four-Dimensional Structure

Selective attention is well known for 2D patterns and perceptual alternations are well established for 3D structures projected into 2D, such as the Necker cube. Here, these concepts are extended to the spatial fourth dimension in the form of the mathematical structure of the 4D hypercube. In orthographic projection, its 2D outline figure has multiple and highly dynamic percepts of up to 28 different 3D interpretations, which correspond to local 3D views of the 4D hypercube. Thus, the spontaneous operations of perceptual processing can provide direct insight into conceptual structure in the fourth dimension.

Presence and Absence of Top and Right Advantage as an Indication of the Attentional Strategies Underlying Object Selection

To explore the conditions in which an object is selected in its entirety and better understand the process underlying such selection, a target, lying on the contour of an outline figure, was judged. Target position on the figure was either known or not known throughout a block of trials, and various properties of the figure itself—continuity, familiarity, and contrast—were manipulated. The pattern of results can best be accounted for by assuming that object selection involves a scan, beginning at the top-right end and terminating only when the bottom-left end is reached. Partial selection could have occurred only for the top and the right positions when the target was known always to be there. As to the manipulated properties, none interacted with knowledge of target position, indicating that they did not affect the process of selection. Most importantly, partial selection was not facilitated even in the discontinuous condition, in which the figure consisted of two separate elements.

Muslim and Judaic-Christian Perceptions of Desirable Body Shape

Undergraduate men, 94 nonUS Muslims and 168 US Judaic-Christians, rated 9 outline figure drawings as like their own current figure, what they would prefer to look like, what figure was most attractive to females, and what female figure they found most attractive. Ratings of the two groups were very similar but the female figure found most attractive was significantly thinner for Judaic-Christian men.

The Performance of Aphasics on Three Automated Perceptual Discrimination Programs

Five aphasics and five controls were compared in their response to three perceptual discrimination programs presented in automated fashion. The programs, composed of shapes based upon those necessary to form English capital letters, were concerned with the variables of shape discrimination, orientation of form, and transition of solid shape to outline figure. Aphasics and controls differed significantly in response latencies and error rates to sets of pre-test items representing each program. Aphasics were given automated training with those programs on whose pre-test they had an error rate greater than 10%. On follow-up testing one week after training, response latency decreased and differed significantly from pre-test latency, and the error rate became comparable to that of the normal controls.

V.—Notes on Phacops Weaveri, Salter

A re-examination of the type-specimens of Phacops Weaveri, Salter, in the Museum of Practical Geology, Jermyn Street, was recently rendered necessary in connection with my palæontological work on the Tortworth Silurian area, the results of which have been published in the November number of the Quarterly Journal of the Geological Society, 1908 (vol. lxiv, pp. 512–545), in a joint paper by Professor S. H. Reynolds and myself. A question had arisen in the course of our work as to the occurrence of this species above the Llandovery Beds, for Salter had stated that some of his figured specimens of pygidia (Mon. Brit. Trilob., pl. iii, figs. 2, 3) came from doubtful Ludlow rocks at Horse-shoe Farm, Tortworth. The species had, however, been founded by him previously on specimens from socalled ‘Caradoc’ [= Llandovery] rocks from Long's Quarry, Tortworth, and an outline figure of the pygidium, apparently a restoration based on the three specimens in Jermyn Street (Nos. 19220, 19221, 19222), had then been given. Subsequently a head-shield from the same quarry was figured in his monograph (pl. iii, fig. 1). It is clear that Salter based the species mainly on the pygidial characters, for the head-shield is dismissed with a few inadequate remarks, its resemblance to Ph. caudatus being considered to be very close. The original description given by Salter in 1849 runs as follows:—“P. laevis, capite quam in P. caudato, nisi lobis glabellae tumidioribus;—caudâ triangulari, ferè aequilatera, convexa, apice acuto haud mucronato, axi 13–16 annulate, costis lateralibus 10–12, simplicibus, vix curvatis, ad marginem aequalem angustum abruptè terminatis.” In the diagrammatic figure of the pygidium which accompanied this description only 12 or 13 rings are indicated on the axis and 10 or 11 ribs on the lateral lobes, which might incline us to think that an immature individual was chosen for the figure, since Salter in his remarks on the species says (op. cit.) that “young specimens have not the full number of ribs”, but no mention that this is the case is found in the explanation of the plate. In Salter's subsequent work (Mon. Brit. Trilob., p. 58) the tail is described as “broad-triangular, wider than long; the sides a little convex; the apex short-mucronate; the axis narrow, conical, ribbed by about sixteen rings; the sides very convex with nine to ten arched simple ribs scarcely at all interlined; the margin [= border] narrow, smooth”. The italics in this quotation are mine, as the number of ribs is fewer than that given in his earlier definition of the species. It may here be remarked that Salter in his monograph reproduces verbatim the definition of the species published in the decades, with the addition of the word trigono with reference to the head before the word nisi, and with the insertion of the epithet multicostata after the word œquilatera in the description of the pygidium.

Contributions to the physiology of vision.— Part the first . On some remarkable and hitherto unobserved phenomena of binocular vision

The author first shows that the perspective projections of an object upon the two retinæ differ according to the distance at which the object is placed before the eyes; if it he placed so distant that to view it the optic axes must be parallel, the two projections are precisely similar; but if it be placed so near that to regard it the optic axes must converge, a different perspective projection is presented to each eye; and these perspectives become more dissimilar as the convergence of the optic axes becomes greater. Notwithstanding this dissimilarity between the two pictures, which is in some cases very great, the object is still seen single; contrary to the very prevalent metaphysical opinion, that the single appearance of objects seen by both eyes is owing to their pictures falling on corresponding points of the two retina;. After establishing these principles, the author proceeds to ascertain what would result from presenting the two monocular perspectives, drawn on plane surfaces, to the two eyes, so that they shall fall on the same parts of the two retinæ as the projections from the object itself would have fallen. Several means are described by which this may be accomplished; but the author especially recommends for this purpose an apparatus called by him a stereoscope , which enables the observer to view the resulting appearances without altering the ordinary adaptation of the eyes, and therefore without subjecting these organs to any strain or fatigue. It consists of two plane mirrors with their backs inclined to each other at an angle of 90°, near the faces of which the two monocular pictures are so placed that their reflected images are seen bv the two eyes, one placed before each mirror, in the same place; the apparatus has various adjustments by means of which the magnitude of the images on the retinæ may be varied, and the optic axes differently converged. If the two monocular pictures be thus presented one to each eye, the mind will perceive, from their combined effect, a figure of three dimensions, the exact counterpart of the object from which the pictures were drawn; to show that this curious illusion does not in the least depend on shading or colouring, the illustrations principally employed are simple outline figures, which give for their perceived resultants skeleton forms of three dimensions. Each monocular outline figure is the representation of two dissimilar skeleton forms, one being the form which it is intended to represent, and another, which Prof. Wheatstone calls its converse figure Viewed by one eye alone the outline may with equal ease be imagined to be either; but when the two monocular pictures are viewed one by each eye, the proper or the complemental form may be fixed in the mind; the former, if the right and left pictures be presented respectively to the right and left eyes; and the latter, if the right picture be presented to the left eye, and the left picture to the right eye. Many new experiments are then detailed, and a variety of instances of false perception of visual objects, some new, others formerly observed, are traced to these principles; among others, the well-known apparent conversion of cameos into intaglios. The author next proceeds to show that pictures similar in form but differing in magnitude within certain limits, when presented one to each eye, are perceived by the mind to be single and of intermediate size; and also that when totally dissimilar pictures, which cannot be combined by the mind into the resemblance of any accustomed objects, are presented one to each eye, they are in general not seen together, but alternately. The memoir concludes with a review of the various hypotheses which have been advanced to account for our seeing objects single with two eyes; and the author states his views respecting the influence which these newly developed facts are calculated to have on the decision of this much debated question.