The attentional blink is governed by a temporary loss of control

Identification of the second of two brief targets is impaired at intertarget lags of less than about 500 msec. We compared two accounts of thisattentional blink (AB) by manipulating the number of digit distractors—and hence the lag—inserted among three letter targets in a rapid serial visual presentation stream of digit distractors. On the resource-depletion hypothesis, longer lags provide more time for processing the leading target, thus releasing resources for the trailing target. On the temporary-loss-of-control (TLC) hypothesis, intervening distractors disrupt the current attentional set, producing a trailing-target deficit. Identification accuracy for trailing targets was unimpaired not only at lag 1 (conventional lag 1 sparing) but also at later lags, if preceded by another target. The results supported the TLC hypothesis but not the resource-depletion hypothesis. We conclude that the AB is caused by a disruption in attentional set when a distractor is presented while the central executive is busy processing a leading target.     

The attentional blink is not a unitary phenomenon

Identification of the second of two targets is impaired if it is presented less than about 500 ms after the first. Three models of this second-target deficit, known as attentional blink (AB), were compared:resource-depletion, bottleneck, and temporary loss of control (TLC). Five experiments, in which three sequential targets were inserted in a stream of distractors, showed that identification accuracy for the leading target depended on an attentional switch whose magnitude varied with distractor–target similarity. In contrast, accuracy for the trailing target depended on similarity between the target and the trailing mask. These results strongly suggest that the AB is not a unitary phenomenon. Resource-depletion was ruled out as a viable account. The effect of attentional switching was handled naturally by the TLC model, while bottleneck models offered the best account of the effect of backward masking.     

Quantitative measurement of handwriting in the assessment of drug-induced parkinsonism

Monitoring drug-induced side effects is especially important for patients who undergo treatment with antipsychotic medications, as these drugs often produce extrapyramidal side effects (EPS) resulting in movement abnormalities similar to parkinsonism. Scientists have developed several objective laboratory tests to measure and research drug-induced movement disorders, but equipment and tests are complex and costly and have not become accepted in large-scale, multi-site clinical trials. The goals of this study were to test whether a simple handwriting measure can discriminate between individuals with psychotropic-induced parkinsonism, Parkinson's disease, and healthy individuals, and to examine some of the psychometric properties of the measure. We examined pen movement kinematics during cursive writing of a standard word in 13 patients with idiopathic Parkinson's disease (PD), 10 schizophrenia patients with drug-induced parkinsonism (SZ), and 12 normal healthy control participants (NC). Participants were instructed to write the word "hello" in cursive twice, at three vertical height scales. Software was used for data acquisition and analysis of vertical stroke velocities, velocity scaling, and smoothness. There were four important results from this study: (1) both SZ patients with drug-induced EPS and PD participants exhibited impaired movement velocities and velocity scaling; (2) performance on the velocity scaling measure distinguished drug-induced EPS from normal with 90% accuracy; (3) SZ, but not PD participants displayed abnormalities in movement smoothness; and (4) there was a positive correlation between age and magnitude of the velocity scaling deficit in PD participants. This study demonstrates that kinematic analyses of pen movements during handwriting may be useful in detecting and monitoring subtle changes in motor control related to the adverse effects of psychotropic medications.     

System reconfiguration, not resource depletion, determines the efficiency of visual search

We examined two theories of visual search: resource depletion, grounded in a static, built-in brain architecture, with attention seen as a limited depletable resource, and system reconfiguration, in which the visual system is dynamically reconfigured from moment to moment so as to optimize performance on the task at hand. In a dual-task paradigm, a search display was preceded by a visual discrimination task and was followed, after a stimulus onset asynchrony (SOA) governed by a staircase procedure, by a pattern mask. Search efficiency, as indexed by the slope of the function relating critical SOA to number of distractors, was impaired under dual-task conditions for tasks that were performed efficiently (shallow search slope) when done singly, but not for tasks performed inefficiently (steep slope) when done singly. These results are consistent with system reconfiguration, but not with resource depletion, models and point to a dynamic, rather than a static, architecture of the visual system.     

GPS analysis of human locomotion: further evidence for long-range correlations in stride-to-stride fluctuations of gait parameters

During free walking, gait is automatically adjusted to provide optimal mechanical output and minimal energy expenditure; gait parameters, such as cadence, fluctuate from one stride to the next around average values. It was described that this fluctuation exhibited long-range correlations and fractal-like patterns. In addition, it was suggested that these long-range correlations disappeared if the participant followed the beep of metronome to regulate his or her pace. Until now, these fractal fluctuations were only observed for stride interval, because no technique existed to adequately analyze an extended time of free walking. The aim of the present study was to measure walking speed (WS), step frequency (SF) and step length (SL) with high accuracy (<1 cm) satellite positioning method (global positioning system or GPS) in order to detect long-range correlations in the stride-to-stride fluctuations. Eight participants walked 30 min under free and constrained (metronome) conditions. Under free walking conditions, DFA (detrended fluctuation analysis) and surrogate data tests showed that the fluctuation of WS, SL and SF exhibited a fractal pattern (i.e., scaling exponent alpha: 0.5 < alpha < 1) in a large majority of participants (7/8). Under constrained conditions (metronome), SF fluctuations became significantly anti-correlated (alpha < 0.5) in all participants. However, the scaling exponent of SL and WS was not modified. We conclude that, when the walking pace is controlled by an auditory signal, the feedback loop between the planned movement (at supraspinal level) and the sensory inputs induces a continual shifting of SF around the mean (persistent anti-correlation), but with no effect on the fluctuation dynamics of the other parameters (SL, WS).     

Differences in heaviness in relation to density and weight

Eight Ss (Group L) judged differences in heaviness between all pairs of stimuli in three series of five weights each, in the range of 100–300 g, presented randomly. Series L varied in weight and density, Series LVW varied only in weight, and Series LVD varied only in density. Another eight Ss (Group H) judged heaviness differences between all pairs of stimuli in three similar series (H, HVW, and HVD) in the range 700–900 g. Differences in density alone yielded relatively greater impressions of difference in heaviness in Group H than in Group L. Predictions from Ross and Di Lollo’s vector theory were confirmed.     

A consistent failure of the power law for lifted weight

The apparent size of squares was determined as a function of physical area and of surface complexity using the method of magnitude estimation. Apparent area increases as a power function of physical area with a slope of about 0.90. The judged areas also increased as a function of complexity of patterns upon the surface, the most complex surfaces being judged approximately 30% larger than the most simple surfaces.     

The Effect of a Discrete Signal on Context Conditioning: Assessment by Preference and Freezing Tests

Four experiments with rats assessed conditioning to contextual cues after the delivery of footshocks that were either signaled by a discrete stimulus or unsignaled. Two different tests were used. The first was a context preference test in which subjects were allowed to move freely in a brightly lit, unconditionally aversive context and the former shock context. The second test consisted of scoring freezing behavior while the animals were confined to the former conditioning context. During context preference tests, signaled-shock animals spent more time in the conditioning context and/or entered that context more frequently than did unsignaled-shock subjects. However, freezing tests largely failed to detect a difference between groups. These results were discussed in terms of possible interactions between the formation of context-shock, signal-shock, and context-signal associations and their effect on performance in each of the two types of tests.