Stimulus probability and prediction outcome as determinants of choice reaction time: Some procedural considerations

Effects of stimulus probability and prediction outcome on two-choice reaction speed (CRS) were determined when a frequency imbalance was reversed half-way through 300 samples of a 70/30 stimulus distribution and when the same 70/30 distribution was sampled for 1200 trials. Prior to each presentation Ss made a prediction; following each presentation Ss identified the stimulus by pressing a right-hand or left-hand trigger. CRS was faster to correctly predicted stimuli, and faster to the more probable stimulus. Ss who were informed of the frequency imbalance reacted significantly faster than Ss who were not. Both practice and boredom effects were demonstrated by using the extended number of trials. CRS was faster during the second session of 300 trials than during the first; after two sessions, CRS was slower during the second half of two additional sessions.     

The Mezzich MMPI regression formula revisited

In a sample of depressed psychiatric inpatients, the Mezzich regression formula, based on five MMPI scales, correlated moderately with clinicians' judgments and yielded few false negative diagnoses in identifying patients with unipolar Major Depressive Disorder, but was less effective in eliminating false positives.     

A revised analysis of the role of efference in motion perception

The analysis of motion perception historically has included efferent as well as afferent mechanisms to account for the perception of motion during eye movement. The application of efferent mechanisms to motion perception has been limited, however, by several illusions which are apparently inconsistent with the notion that oculomotor mechanisms contribute to motion perception. An alternative account is presented of the manner in which efference may contribute to the perception of motion. It is proposed that distinct smooth eye-movement systems contribute differentially to object motion perception. Specifically, activity in the smooth pursuit system gives rise to the perception of object motion, whereas activity in the smooth component of reflexive eye movements does not. Tracking of a moving object results in object motion perception as a result of efference in the pursuit system. However, the pursuit system may be activated to oppose the smooth component of reflexive eye movements in order to preserve fixation on a stationary object. In such cases neither the fixated object nor the eye is moving but illusory movement results from the efference in the pursuit system. A number of illusory movement phenomena are interpreted in terms of this model.     

Single-component microcomputer-driven assessment of attention

The Gordon Diagnostic System (GDS) is a single-component microcomputer-based instrument that can be used to administer 11 psychological tests. The game-like tasks provide objective data for evaluating possible attention-deficit hyperactivity disorder or other conditions that affect a person’s ability to sustain attention and exert self-control. The core of the instrument is an integrated circuit with a microprocessor, a random access memory, and an erasable, programmable read-only memory (EPROM). It can be programmed with an IBM PC and an EPROM programmer. The assembly language source is compiled into machine language, which is used to simulate the GDS on the IBM PC or is “burned” into the ROM. The memory is erasable with ultraviolet light, so revisions can be made easily. The GDS illustrates that “custom” programming a ROM is not limited to large industrial concerns, and that it can be done within small research groups.     

The relationship between perceived length and egocentric location in Müller-Lyer figures with one versus two chevrons

We examined the apparent dissociation of perceived length and perceived position with respect to the Müller-Lyer (M-L) illusion. With the traditional (two-chevron) figure, participants made accurate open-loop pointing responses at the endpoints of the shaft, despite the presence of a strong length illusion. This apparently non-Euclidean outcome replicated that of Mack, Heuer, Villardi, and Chambers (1985) and Gillam and Chambers (1985) and contradicts any theory of the M-L illusion in which mislocalization of shaft endpoints plays a role. However, when one of the chevrons was removed, a constant pointing error occurred in the predicted direction, as well as a strong length illusion. Thus, with one-chevron stimuli, perceived length and location were no longer completely dissociated. We speculated that the presence of two opposing chevrons suppresses the mislocalizing effects of a single chevron, especially for figures with relatively short shafts.