Preattentive vision and perceptual groups

Recent evidence suggests that preattentive processing may not be limited to the analysis of simple stimulus features as previously suggested. To explore this idea a visual search task was used to test whether the shapes of several perceptual groups can be processed in parallel. Textured displays that give rise to strong perceptual grouping were used to create figures on a background. Search times for a target figure distinguished by a unique shape were found to be independent of the number of distractor figures in the display. This result indicates that perceptual groups may be processed in parallel and suggests an expanded role for preattentive processing in vision.     

Sensitivity and decisional factors in the psychological refractory period

Three trained Ss responded to a pair of events presented at fixed interstimulus intervals (ISIs) of 33, 67, and 100 msec. Each event was the independent presence of a visual stimulus (S-P) or its absence (S-A), to which Ss were to respond or not, with a set for speed over accuracy. The probabilities of Sop occurrence [P(S)] to each of the events were varied. Pretrial verbal reports or behavioral hypotheses (BHs) werealso obtained. P(S), ISI, BH, and order (first vs second event) were all generally determinants of both RT to Sop and inhibition probability to S-A. However, when the RT data were corrected for inhibition probability, order was the only systematic effect that remained. The results were discussed in terms of approaches to the psychological refractory period derived from signal detection theory involving differential sensitivity as opposed to criterion.     

Graphics software and hardware for RT-11 systems

A general-purpose graphics package is described that allows the user to generate figures with a supraset of the basic CalComp plotting subroutines. The software runs under RT-11 on an LSI-11 with 28K words of memory. The graphics subroutine library is approximately 200 blocks long. The plotting tasks are passed over an RS 232 line to a simple extension of an inexpensive and commercially available graphics controller. The controller implements these tasks as plotting instructions to a color television, a vector display, and a digital plotter. The graphics subroutines are written in FORTRAN and are invoked by the user as subroutine calls from a FORTRAN program. The graphics controller is a modified Motorola “Micro Chroma 68 Kit.” The board is based on the 6808 microprocessor and 6847 video controller. It provides eight graphic modes from 64 by 32 eight-color graphics to 128 by 192 four-color graphics to 256 by 192 two-color graphics. The present software and hardware implements the graphics subroutines as 256 by 192 two-color graphics, as 512 by 512 vector graphics, and as stepping instructions for a digital plotter.     

Interocular transfer of visual aftereffects

A number of the well-known visual after-effects of adaptation exhibit interocular transfer, so that presentation of an adaptation figure to one eye produces a temporary change in the performance of the nonadapted eye. This outcome is usually attributed to the involvement of binocular visual neurons that respond to stimulation of either eye. The fact that interocular transfer is incomplete (i.e., the transferred aftereffect is smaller in magnitude than that induced and measured in the same eye) is routinely cited as evidence for the involvement of monocular neurons. This article critically examines these two interpretations, which are developed in terms of a neural model of interocular transfer. No evidence, logical or empirical, was obtained for rejecting the model. Our analysis further shows that the model must assume some type of pooling process that operates over all tested neurons, both adapted and unadapted. Finally, general implications of the interocular transfer model are discussed, the aim being to delimit the conclusions that may be drawn from interocular transfer experiments.     

MacPsych: An electronic discussion list and archive for psychology concerning the Macintosh computer

MacPsych is an electronic mail discussion list and an electronic archive for those using the Macintosh in psychology. The discussion list allows psychologists from around the world to ask questions and discuss issues relating to the use of the Macintosh in psychology. The archive is a place where list members may share software and other files of relevance. The Society for Computers in Psychology sponsors the discussion list, and the journalBehavior Research Methods, Instruments, & Computers has designated the archive as the distribution site for Macintosh software and files described in its pages. Those interested may join the list by sending electronic mail to macpsych-request@stolaf.edu. The archive can be accessed via anonymous ftp at ftp.stolaf.edu in the directory pub/macpsych.     

Death by hand grenade: altruistic suicide in combat

Durkheim's theory of suicide is examined as it bears on the concept of altruistic suicide. A subtype called heroic altruistic suicide or self-sacrifice is identified. Relationships are hypothesized between cohesion and self-sacrifice and rank and self-sacrifice, and they are tested in combat situations, utilizing official published information on the Congressional Medal of Honor. Altruistic suicide is found to be higher in more cohesive than in less cohesive groups and more likely among enlisted men than among career officers and noncommissioned officers. In addition to testing hypotheses empirically, this study elaborates Durkheim by extending his analysis of altruistic suicide and clarifies his work by delineating sources of error in his hypotheses.     

Tachistoscopic perception under head tilt

Subjects attempted to identify singly presented letters, flashed briefly at six different locations equidistant from fixation. The locations were at 1, 3, 5, 7, 9, and 11 o’clock on an imaginary circle. The subjects performed both with their heads upright or tilted 60° (i.e., through 2 and 8 o’clock or through 10 and 4 o’clock). In Experiment 1, the letters were projected in a gravitationally fixed rectangular surround, and accuracy of report depended largely on the locations of the letters in gravitational coordinates, although there was clear evidence of a retinal influence as well. In Experiment 2, the surround was circular and accuracy depended principally on retinal location, although there was also a gravitational influence. Analysis of individual data suggested that, when their heads were tilted, subjects generally adopted a reference frame which lay between the retinal and gravitational frames, closer to one than the other but typically coinciding with neither. We conclude that the subjective reference frame does not depend on a poststimulus correction, but rather that stimulus information is incorporated directly into the subjective frame. The data also suggested that lateral asymmetries depend on a perceptual rather than a retinal interpretation of left and right visual fields.