Heading and path information from retinal flow in naturalistic environments

In four experiments, we explored the heading and path information available to observers as we simulated their locomotion through a cluttered environment while they fixated an object off to the side. Previously, we presented a theory about the information available and used in such situations. For such a theory to be valid, one must be sure of eye position, but we had been unable to monitor gaze systematically; in Experiment 1, we monitored eye position and found performance best when observers fixated the designated object at the center of the display. In Experiment 2, when we masked portions of the display, we found that performance generally matched the amount of display visible when scaled to retinal sensitivity. In Experiments 3 and 4, we then explored the metric of information about heading (nominal vs. absolute) available and found good nominal information but increasingly poor and biased absolute information as observers looked farther from the aimpoint. Part of the cause for this appears to be that some observers perceive that they have traversed a curved path even when taking a linear one. In all cases, we compared our results with those in the literature.     

The effect of spatial frequency on global precedence and hemispheric differences

There are many conditions in which identification proceeds faster for the global form of a hierarchical pattern than for its local parts. Since the global form usually contains more lower spatial frequencies than do the local forms, it has frequently been suggested that the higher transmission rate of low spatial frequencies is responsible for the global advantage. There are also functional hemispheric differences. While the right hemisphere is better at processing global information, the left hemisphere has an advantage with respect to local information. In accordance with the spatial-frequency hypothesis, it has been speculated that this difference is due to a differential capacity of the hemispheres for processing low and high spatial frequencies. To test whether low spatial frequencies were responsible for the global advantage and/or for the observed hemispheric differences, two experiments were carried out with unfiltered and highpass-filtered compound-letter stimuli presented at the left, right, or center visual field. The first experiment, in which the target level was randomized in each trial block, revealed that low spatial frequencies were not necessary for either global advantage or for hemispheric differences. Highpass filtering merely increased the response times. In the second experiment, the target level was held constant in each block. This generally increased the speed of responding and produced interactions between filtering and global-local processing. It was concluded that both sensory and attentional or control mechanisms were responsible for global precedence and that the hemispheres differed with respect to the latter.     

Exploring the sexual world of the unemployed adolescent

Unemployed adolescents may be at substantial risk of the negative consequences of sexuality. This study investigated the sexual perceptions and practices of 125 unemployed adolescents. Gender, but not age, differences were found in sexual perceptions and practices. Overall, this sample was engaging in high levels of sexual activity with a low rate of condom use.     

Magnitude of luminance modulation specifies amplitude of perceived movement

A compelling impression of movement, which is perceptually indistinguishable from a real displacement, can be elicited by patterns containing no spatially displaced elements. An apparent oscillation, w-movement, was generated by a stationary pattern containing a large number of horizontal pairs of spatially adjacent dots modulated in brightness. The observer’s task was to adjust the perceived amplitude of the w-motion to match the amplitude of a real oscillation. All of the data can be accounted for by a simple rule: If the relative change in the luminance,W = αL/L, between two adjacent stationary dots is kept constant, the distance over which these dots appeared to travel in space comprises a fixed fraction of the total distance by which they are separated. The apparent amplitude of the w-motion increases strictly in proportion with luminance contrast, provided that the contrast is represented in the motion-encoding system by a rapidly saturating compressive Weibull transformation. These findings can be explained in terms of bilocal motion encoders comparing two luminance modulations occurring at two different locations.     

Temporal coordination of alternative and simultaneous aiming movements of constrained timing structure

Two experiments are reported addressing the preparation and initiation of movements with equal or unequal timing properties for both hands. Temporal coordination was examined in two movement tasks: one in which both hands performed the movements simultaneously (simultaneous aiming task) and one in which only one alternative of two possible movements was executed (choice aiming task). For each task a different group of subjects was used. Besides the timing relationships between both movements, the effects of preparation interval (1, 3, and 5 s), the average velocity (7, 14, 17.5, and 70 cm/s), the presence of advance information about the required velocity of the movement(s), and practice were investigated. Based on the common- and the specific-timing notions, distinct hypotheses were tested as to the effects of the variables on the temporal coordination as revealed by reaction time. A main result was that the effects of timing differences between the hands was task specific. For the choice task the data are in agreement with the common-timing notion of coordination, i. e., only one timing demand at a time can be prepared, whereas in the simultaneous task evidence was obtained for the specific-timing notion, i. e., independent preparation and initiation of different timing properties for the hands. However, it is argued that the results of the choice task probably do not reflect a general inability to prepare movements of different timing requirements for both hands, but is related to a task-specific strategy of selective preparation.     

Does stimulus correspondence account for the Simon effect? Comments on Hasbroucq and Guiard (1991)

Summary In a recent paper analysing the Simon effect, Hasbroucq and Guiard (1991) concluded that stimulus congruence, a correspondence relationship between stimulus components, accounts for the Simon effect and explains its reversal in the Hedge and Marsh experiment (1975). We contend that their definition of stimulus congruence is applied inconsistently, which invalidates their conclusion. It is argued here that the effect of display-control arrangement correspondence (Simon, Sly, & Vilapakkam, 1981) is an alternative account that fits the presented data better. In a second experiment, Hasbroucq and Guiard (1991) claimed to have invalidated the suggestion that display-control arrangement correspondence could be considered to be an alternative account of the findings in their Experiment 1. However, we assert that the type of display-control arrangement employed in their second experiment was so unpredictable that no effect of display-control arrangement correspondence could occur.     

Influence and development: Two basic paradigms of education

The article discusses two basic paradigms of western educational theory, namely the concept of “influence” and the concept of “development”. Two historical contextes are analyzed, John Locke's theory of human learning and Jean-Jacques Rousseau's theory of natural development. Both theories are rejected in favour of a position beyond “influence” and “development”. This position of a theory of education (Erziehung) is marked with the term “moral communication”.