Sensitivity to initial values in full non‐parametric maximum‐likelihood estimation of the two‐parameter logistic model

Parameters of the two‐parameter logistic model are generally estimated via the expectation–maximization (EM) algorithm by the maximum‐likelihood (ML) method. In so doing, it is beneficial to estimate the common prior distribution of the latent ability from data. Full non‐parametric ML (FNPML) estimation allows estimation of the latent distribution with maximum flexibility, as the distribution is modelled non‐parametrically on a number of (freely moving) support points. It is generally assumed that EM estimation of the two‐parameter logistic model is not influenced by initial values, but studies on this topic are unavailable. Therefore, the present study investigates the sensitivity to initial values in FNPML estimation. In contrast to the common assumption, initial values are found to have notable influence: for a standard convergence criterion, item discrimination and difficulty parameter estimates as well as item characteristic curve (ICC) recovery were influenced by initial values. For more stringent criteria, item parameter estimates were mainly influenced by the initial latent distribution, whilst ICC recovery was unaffected. The reason for this might be a flat surface of the log‐likelihood function, which would necessitate setting a sufficiently tight convergence criterion for accurate recovery of item parameters.     

Disentangling the adult attention-deficit hyperactivity disorder endophenotype: parametric measurement of attention

Attention deficit hyperactivity disorder (ADHD) persists frequently into adulthood. The decomposition of endophenotypes by means of experimental neuro-cognitive assessment has the potential to improve diagnostic assessment, evaluation of treatment response, and disentanglement of genetic and environmental influences. We assessed four parameters of attentional capacity and selectivity derived from simple psychophysical tasks (verbal report of briefly presented letter displays) and based on a "theory of visual attention." These parameters are mathematically independent, quantitative measures, and previous studies have shown that they are highly sensitive for subtle attention deficits. Potential reductions of attentional capacity, that is, of perceptual processing speed and working memory storage capacity, were assessed with a whole report paradigm. Furthermore, possible pathologies of attentional selectivity, that is, selection of task-relevant information and bias in the spatial distribution of attention, were measured with a partial report paradigm. A group of 30 unmedicated adult ADHD patients and a group of 30 demographically matched healthy controls were tested. ADHD patients showed significant reductions of working memory storage capacity of a moderate to large effect size. Perceptual processing speed, task-based, and spatial selection were unaffected. The results imply a working memory deficit as an important source of behavioral impairments. The theory of visual attention parameter working memory storage capacity might constitute a quantifiable and testable endophenotype of ADHD.     

Objects do not aid inhibition of return in crossing the vertical meridian

Location-based cuing experiments have shown that inhibition of return (IOR) spreads beyond a cued location but appears to be confined to the cued hemifield by the vertical meridian. Previous studies have also shown that IOR can spread across objects and here we investigate whether an object can be used to mediate the spreading of IOR into the opposite hemifield. Two experiments used a rectangular object that surrounded four target locations, two to the left and right of a central fixation point. The spreading of IOR in the presence of the object was determined and compared with a condition where the object-frame was absent. Object-present and object-absent trials were either mixed within a block (Experiment 1) or divided into separate blocks (Experiment 2). Both experiments revealed robust inhibition in the cued but not the uncued hemifield, further demonstrating the hemifield-based spreading of IOR.     

Bimanual response grouping in dual-task paradigms

In three experiments we measured response time (RT) and peak force (PF) to investigate the grouping of left- and right-hand key press responses in a dual-task paradigm involving two independent go/no-go tasks. Within each task, a go stimulus within one of two modalities (i.e., visual versus auditory) required a response by one hand. In Experiment 1 with simultaneous go stimuli in the two tasks, responses appeared to be grouped in approximately 75-80% of trials, compared with nearly 100% grouping in a single-task condition requiring bimanual responses to the onset of any stimulus in either modality. In Experiment 2 with stimulus onset asynchronies (SOAs) of 0-400 ms between the two go stimuli, response grouping clearly declined as SOA increased, although some grouping was still evident even at the longest SOA. The same pattern was observed in Experiment 3 with the same range of SOAs but unpredictable stimulus order, suggesting that grouping is not strongly dependent on prior knowledge of the likely response order. These results emphasize the pervasiveness of response grouping in bimanual dual-task RT paradigms and provide useful clues as to its nature.     

Inferences under time pressure: how opportunity costs affect strategy selection

Do the inference strategies people select depend on the magnitude of time pressure? Is this dependency modified by the type of time pressure? These questions are addressed in three experimental studies in which participants made inferences after having searched for information on a computerized information board. In Study 1, time pressure was induced indirectly by imposing opportunity costs of being slow, a form of time pressure that is common in daily life but that has rarely been examined in the literature. A simple lexicographic heuristic (LEX) achieved the best fit in predicting participants' inferences. Studies 2 and 3 induced high time pressure either indirectly by imposing opportunity costs in terms of time or directly by limiting the time for each choice. Regardless of how time pressure was induced, under high time pressure the inferences could be best predicted with LEX, whereas under low time pressure a weighted linear model that integrates all available information predicted the inferences best. We conclude that people select strategies adaptively depending on characteristics of the situation.     

Cognitive resources, valence, and memory retrieval of emotional events in older adults

In 2 studies with older adults, the authors investigated the effect of executive attention resources on the retrieval of emotional public events. Participants completed a battery of working memory tasks, as a measure of executive attention, and a battery of tasks assessing memory, as well as subjective experiences associated with the retrieval of remote public events. Participants also rated the valence of each public event story. The group-rated valence of the public event stories predicted retrieval and the quality of experiences associated with them, such that emotionally arousing events elicited the highest memory rates and the richest experiences. Furthermore, positive public events elicited the highest memory rates. Executive attention moderated only the relationship between event valence and how participants' associated memories are experienced at retrieval, such that superior executive attention resources predicted richer experiences associated with positive relative to neutral and negative stories. The current results extend previous findings on the effects of aging on emotion regulation, suggesting that cognitive control resources modulate subjective experiences associated with retrieved memories for remote real life events, but not memory retrieval itself. (PsycINFO Database Record (c) 2008 APA, all rights reserved).