Stress reactivity and coping in seasonal and nonseasonal depression

Stress, stress reactivity, and coping skill use were examined in individuals with seasonal depression, nonseasonal depression, and nondepressed controls. Although participants in the two depressed groups reported using more avoidance coping strategies than controls, only participants in the seasonal depressed group reported using more season-specific coping (i.e., light-related strategies) than participants in the nonseasonal depressed and control groups. Individuals in the seasonal depressed group also reporting using acceptance coping strategies less frequently than individuals in the control group. Only participants in the nonseasonal depressed group, however, exhibited greater psychophysiological arousal in reaction to a laboratory stressor (i.e., unsolvable anagram task) when compared to participants in the seasonal and nondepressed control groups. Participants in both depressed groups reported greater impact of negative life events during the past 6 months than did controls. Similarities and differences in the two types of depression may have implications for the conceptualization and treatment of seasonal depression.     

Top-down inhibition of search distractors in parallel visual search

In three experiments, we examined distractor inhibition in parallel ("pop-out") visual search. Distractor inhibition was measured in terms of reaction time (RT) to a simple luminance increment probe presented, after the search task response, at display locations that either contained a search distractor (on-probe) or were blank (off-probe). When the search stimuli remained in view, the on-probe (relative to off-probe) RT cost was larger than in a baseline condition in which observers had only to passively view, rather than search, the display. This differential on-probe RT cost, which discounts effects of masking, was interpreted as a measure of distractor inhibition associated with target selection in parallel visual search. Taken together, the results argue that the distractor inhibition is an object-based and local phenomenon that affects all distractors (of a particular type) in an equal manner.     

Decomposition of variability in the execution of goal-oriented tasks: three components of skill improvement

A central ability of the motor system is to achieve goals with great reliability, although never with zero variability. It is argued that variability is reduced with practice by 3 separate means: reduction of stochastic noise (N), exploitation of task tolerance (T), and covariation (C) between central variables. A method is presented that decomposes variability into these components in relation to task space that is defined by the execution variables. Successful variable combinations form the solution manifold. In a virtual skittles task, it is demonstrated that participants' improvement over repetitions, indicated by increasing accuracy, is accounted for by N, T, and, to a lesser degree, C. The relative contribution of these components changes over the course of practice and task variations.     

The dynamics of operations in visual memory: a review and new evidence for oscillatory priming

Evidence from neurophysiological studies indicates that the synchronization of distributed neuronal assemblies in the gamma frequency range is responsible for the integration of discrete stimulus components into coherent wholes (e.g., see Singer, 1999 for review). Psychophysical support for this hypothesis has been reported in experiments that demonstrate that the presentation of a synchronous-premask frame within a 40-Hz flickering premask matrix primes the subsequent detection of a target Kanizsa-type square by generation of a 40-Hz prime (Elliott & Müller, 1998). Psychopharmacological and electrophysiological evidence suggests that this priming mechanism is related to activity in interneuronal networks and relies on the combined function of prefrontal and posterior circuits. In addition, psychophysical experiments demonstrate the existence of a prime-specific visual short-term memory that oscillates at 40 Hz and remains functional for up to 300 ms post-stimulus offset. These results are consistent with a view of the prime as a form of oscillatory mechanism, related to the persistence of visual information (Coltheart, 1980) and in the capacity guided by (prefrontal) top-down influences upon visual-cortical function.     

Visual search for singleton feature targets across dimensions: Stimulus- and expectancy-driven effects in dimensional weighting

Four pop-out search experiments investigated whether dimension-based visual attention is top-down modulable. Observers searched for singleton feature targets defined, variably across trials, by a color or an orientation difference to nontargets. Observers were precued to the most probable target-defining dimension (e.g., by the word color) or feature (red) on a given trial. Results revealed expedited reaction times (RTs) for valid-dimension targets relative to neutral-cue conditions, and slowed RTs for invalid-dimension targets. Cue information as to precise target feature yielded some extra effect only for color targets. The dimensional cuing significantly reduced, but did not abolish, the dimension-specific influence of the previous target on detection of the current target (same-dimension RT < different-dimension RT). These findings confirm that top-down dimensional set modulates stimulus-driven dimension processes in the detection of pop-out signals. ((c) 2003 APA, all rights reserved)     

It looks easy! Heuristics for combinatorial optimization problems

Human performance on instances of computationally intractable optimization problems, such as the travelling salesperson problem (TSP), can be excellent. We have proposed a boundary-following heuristic to account for this finding. We report three experiments with TSPs where the capacity to employ this heuristic was varied. In Experiment 1, participants free to use the heuristic produced solutions significantly closer to optimal than did those prevented from doing so. Experiments 2 and 3 together replicated this finding in larger problems and demonstrated that a potential confound had no effect. In all three experiments, performance was closely matched by a boundary-following model. The results implicate global rather than purely local processes. Humans may have access to simple, perceptually based, heuristics that are suited to some combinatorial optimization tasks.     

Evidence of separable spatial representations in a virtual navigation task

Three experiments investigated spatial orientation in a virtual navigation task. Subjects had to adjust a homing vector indicating their end position relative to the origin of the path. It was demonstrated that sparse visual flow was sufficient for accurate path integration. Moreover, subjects were found to prefer a distinct egocentric or allocentric reference frame to solve the task. "Turners" reacted as if they had taken on the new orientation during turns of the path by mentally rotating their sagittal axis (egocentric frame). "Nonturners," by contrast, tracked the new orientation without adopting it (allocentric frame). When instructed to use their nonpreferred reference frame, both groups displayed no decline in response accuracy relative to their preferred frame; even when presented with reaction formats based on either ego or allocentric coordinates, with format unpredictable on a trial, both groups responded highly accurately. These findings support the assumption of coexisting spatial representations during navigation.     

A new learning paradigm elicits fast visual discrimination in pigeons

The authors describe a novel multistimulus, multiple-matching learning paradigm for pigeons, which they believe not only simulates pigeons' natural foraging behavior but also more realistically shows their visual discrimination ability. A touch screen thin film transistor panel shows a stimulus configuration consisting of a 2-dimensional array of bitmap images that changes from trial to trial. The pigeon's task during each trial is to peck at images that are defined as positive by the experimenter. An experiment exploring the ability of pigeons to discriminate between achromatic male and female human faces demonstrated the effectiveness of the procedure. In contrast to 12 pigeons that show little improvement over 60 hr of go/no-go discrimination training, 14 multiple-matching pigeons mastered the problem within a few hours.     

Visual search for dimensionally redundant pop-out targets: parallel-coactive processing of dimensions is location specific

Three visual search experiments investigated redundancy gains for single and dual odd-one-out feature targets that differed from distractors in orientation, color, or both. In Experiment 1, redundant-target displays contained (a) a single target defined in 2 dimensions, (b) dual targets each defined in a different dimension, or (c) dual targets both defined in the same dimension. The redundancy gains, relative to single nonredundant targets, decreased from the first condition on, with violations of J. Miller's (1982) race model inequality (RMI) manifested only in the first 2 conditions. Experiment 2 systematically varied the spatial separation between dual targets each defined in a different dimension. Violations of the RMI were evident only when the 2 targets occupied nearby locations. Experiment 3 provided evidence of RMI violations by dimensionally redundant targets at both precued (likely) and noncued (unlikely) display locations. Taken together, these results suggest that there is coactivation of a common mechanism by target signals in different dimensions (not by signals in the same dimension), that the coactivation effects are spatially specific, and that the coactivated mechanisms are located at a preattentive, perceptual stage of processing.     

On the microstructures of equilibrated and quenched spinel-containing nickel titanates

Electron microscopy has been used to study the microstructures of equilibrated and quenched NiO-TiO₂ mixtures containing 5, 10, 15, 20 and 25wt% TiO₂. All the specimens contained rocksalt- and spinel-structured phases on a nanometre scale. The microstructure suggests that a nonstoichiometric spinel decomposed during quenching. The 25wt% TiO₂ specimen exhibited a lamellar microstructure composed of NiTiO₃ and spinelNiO. These phases had the usual orientation relationships, i.e., (111)_cubic||(0001)_hex and (110)_cubic|| (1100>_hex. Faceted NiO solid-solution regions with coherent cube-on-cube interfaces with the spinel were found in the four specimens of lower TiO₂ contents. When large (15 and 20wt% TiO₂), these regions were faceted cuboidal particles. With lower TiO₂ contents, these regions were no longer equiaxed and could be interconnected. The specimens were chemically homogeneous on a length scale of about 1mum. Morphological evidence is presented to explain which part of the microstructure most probably already existed in this form during equilibration. In particular, the large-scale NiTiO₃ and the spinel lamella in the 25wt% TiO₂ material form during long-term equilibration.