The development of distance estimation in optic flow

In three experiments we tested the ability of children aged 8 to 12 years and adults to locate a target in an optic texture flow projected onto the ground. During the exposure phase, a static target (diode) was lit up at 6 m or 8 m on the ground in front of the subject. During the pointing phase, the subject was asked to indicate the perceived location of the target with a laser pointer as soon as the target was switched off. In the first experiment, during both phases the optic texture (environment) was either motionless or approaching the subject. Results showed that target locations were significantly more underestimated within the moving texture than within the still texture. In the second experiment, a detailed error analysis showed that the differences of performance between children and adults were not due to differences in eye height. Errors can be described by a linear fit with the retinal speed of the optic flow surrounding the targets. Distance judgments improved from the age of 8 years onwards. In the last experiment we found the same kind of results with a receding texture and without stimulation in central vision. Results are discussed in terms of subject's capacity to compensate for the effect of linear vection produced by the optic flow.     

A neural network approach to movement pattern analysis

Movements are time-dependent processes and so can be modelled by time-series of coordinates: E.g., each articulation has geometric coordinates; the set of the coordinates of the relevant articulations build a high-dimensional configuration. These configurations--or "patterns"--give reason for analysing movements by means of neural networks: The Kohonen Feature Map (KFM) is a special type of neural network, which (after having been coined by training with appropriate pattern samples) is able to recognize single patterns as members of pattern clusters. This way, for example, the particular configurations of a given movement can be identified as belonging to respective configuration clusters, where the sequence of clusters to which the time-depending configurations belong, characterizes the process as a 2-dimensional trajectory. The advantages of this method are that: the high dimensionality of the original processes is reduced to two dimensional trajectories, the clusters are automatically determined by the network, and all data for further analyses can automatically be transferred into a data base. Thus, the processes can either be visualized and analysed by an expert or again processed by further automatic analysing tools, as has been done with similarity matrices. The disadvantage is that a KFM-training needs a huge amount of information, which normally is not available from experiments. However, the Dynamically Controlled Network DyCoN (a special type of KFM) makes it possible to reduce the amount of original training data substantially--e.g., by adding stochastically generated ones. Currently, DyCoN is used in several projects in order to generally support analyses of processes in sport. It should be emphasized that the presented approach is not meant to improve the understanding or to develop models of human movement but to give a survey of the advantages and methodological aspects of net-based movement analysis.     

Do behavioral disturbances in persons with Alzheimer's disease predict caregiver depression over time?

Random effects models were used to examine the association between behavioral disturbances in persons with Alzheimer's disease (N = 90) and caregiver depressive symptoms at 2-month intervals over an 18-month period. There was substantial variability in trajectories of change in caregiver depressive symptoms over time but no systematic increase in distress despite increased severity of dementia symptoms. Total behavioral disturbances were associated with higher levels of caregiver depressive symptoms: this effect was primarily attributable to aggressive behaviors. No consistent departure from linearity was evident in the relationship between behavior and depression over time.     

A longitudinal study of implicit and explicit memory in old persons

Decline in explicit memory with advancing age is a common finding, but it is unclear whether implicit memory (repetition priming) declines or remains stable. Meta-analyses of studies that examined differences between extreme groups (young-old), typically at a single point in time and on a single test, suggest that a mild reduction in priming occurs with advancing age. The authors examined explicit memory and priming, on multiple tests over 4 annual data-collection waves, in a large group of older persons without dementia at baseline. Explicit memory declined significantly, but priming remained stable. Findings indicate that explicit memory and priming are dissociable on the basis of age-related change and that mildly reduced priming is not an inevitable consequence of growing older.     

Recognizing one’s own clapping: The role of temporal cues

Do individuals recognize their own clapping? We investigated this question with an off-line paradigm in which the perception of the claps is temporally separated from their generation. In a first experiment, we demonstrated that acoustic recordings of clapping provide sufficient information for discriminating between one’s own performance and that of another participant. Self-recognition was still preserved when the claps were reproduced by uniform tones that only retained their temporal pattern. In a subsequent experiment, we verified that the general tempo provides an important cue for self-recognition. Finally, we showed that self-recognition does not rely on concurrent synchronization of actual movements with the auditory sequences. The results are discussed in the light of current theories about perception-action links.     

Therapy of treatment resistant depression: focus on the management of TRD with atypical antipsychotics

Treatment-resistant depression (TRD) represents a significant challenge for physicians. About one third of patients with major depressive disorder fail to experience sufficient symptom improvement despite adequate treatment. Despite this high occurrence of TRD there was no general consensus on diagnosis criteria for TRD until 1997 when researchers proposed a model of defining and staging TRD. In 1999, others defined operational criteria for the definition of TRD. Treatment of TRD is commonly separated into pharmacologic and nonpharmacologic methods. This review gives a short overview of these two methods. The nonpharmacologic methods include psychotherapy, electroconvulsive therapy, and vagus nerve stimulation. Pharmacologic methods include switching to another antidepressant monotherapy, and augmentation or combination with two or more antidepressants or other agents. This review especially focuses on the augmentation of the antidepressant therapy with atypical antipsychotics.     

Planning of saccadic eye movements

Most theories of the programming of saccadic eye movements (SEM) agree that direction and amplitude are the two basic dimensions that are under control when an intended movement is planned. But they disagree over whether these two basic parameters are specified separately or in conjunction. We measured saccadic reaction time (SRT) in a situation where information about amplitude and direction of the required movement became available at different moments in time. The delivery of information about either direction or amplitude prior to another reduced duration of SRT demonstrated that direction and amplitude were specified separately rather than in conjunction or in a fixed serial order. All changes in SRT were quantitatively explained by a simple growth-process (accumulator) model according to which a movement starts when two separate neural activities, embodying the direction and amplitude programming, have both reached a constant threshold level of activity. Although, in isolation, the amplitude programming was faster than the direction programming, the situation reversed when two dimensions had to be specified at the same time. We conclude that beside the motor maps representing the desired final position of the eye or a fixed movement vector, another processing stage is required in which the basic parameters of SEM, direction and amplitude, are clearly separable.     

The dynamical foundations of motion pattern formation: stability,selective adaptation,and perceptual continuity

A dynamical model is used to show that global motion pattern formation for several different apparent motion stimuli can be embodied in the stable distribution of activation over a population of concurrently activated, directionally selective motion detectors. The model, which is based on motion detectors being interactive, noisy, and self-stabilizing, accounts for such phenomena as bistability, spontaneous switching, hysteresis, and selective adaptation. Simulations show that dynamical solutions to the motion correspondence problem for a bistable stimulus (two qualitatively different patterns are formed) apply as well to the solution for a monostable stimulus (only one pattern is formed) and highlight the role of interactions among sequentially stimulated detectors in establishing the state dependence and, thereby, the temporal persistence of percepts.     

Object-based attentional selection can modulate the Stroop effect

The Stroop (1935) effect is the inability to ignore a color word when the task is to report the ink color of that word (i.e., to say "green" to the word RED in green ink). The present study investigated whether object-based processing contributes to the Stroop effect. According to this view, observers are unable to ignore irrelevant features of an attended object (Kahneman & Henik, 1981). In three experiments, participants had to name the color of one of two superimposed rectangles and to ignore words that appeared in the relevant object, in the irrelevant object, or in the background. The words were congruent, neutral, or incongruent with respect to the correct color response. Words in the irrelevant object and in the background produced significant Stroop effects, consistent with earlier findings. Importantly, however, words in the relevant object produced larger Stroop effects than did the other conditions, suggesting amplified processing of all the features of an attended object. Thus, object-based processing can modulate the Stroop effect.