Absence of an interaction between navigational strategies based on local and distal landmarks

In 3 experiments, rats were required to escape from a Morris pool by swimming to a submerged platform that was located at the apex of a notional, equilateral triangle with 2 different landmarks occupying the corners at the base. Training for 1 group was always conducted in view of the landmarks surrounding the pool and with the triangular array in a fixed orientation. Subjects could therefore identify the direction of the platform from a single landmark within the pool by reference to cues outside the pool or to the other landmark within the pool. Both strategies were used, and the results from additional groups revealed that the first of these strategies did not affect the acquisition of the second one.     

Transfer of spatial behavior between different environments: implications for theories of spatial learning and for the role of the hippocampus in spatial learning

In 3 experiments, rats were required to find a submerged platform located in 1 corner of an arena that had 2 long and 2 short sides; they were then trained to find the platform in a new arena that also had 2 long and 2 short sides but a different overall shape. The platform in the new arena was easier to find if it was in a corner that was geometrically equivalent, rather than the mirror image, of the corner where it had previously been located. The final experiment revealed that hippocampal lesions impaired rats' ability to find the platform in these arenas. The results suggest that rats did not use the overall shape of the arena to locate the platform but relied on more local cues and that the hippocampus plays a role in navigation based on these cues.     

Temporal specificity of extinction in autoshaping

Three experiments investigated the effects of varying the conditioned stimulus (CS) duration between training and extinction. Ring doves (Streptopelia risoria) were autoshaped on a fixed CS-unconditioned stimulus (US) interval and extinguished with CS presentations that were longer, shorter, or the same as the training duration. During a subsequent test session, the training CS duration was reintroduced. Results suggest that the cessation of responding during an extinction session is controlled by generalization of excitation between the training and extinction CSs and by the number of nonreinforced CS presentations. Transfer of extinction to the training CS is controlled by the similarity between the extinction and training CSs. Extinction learning is temporally specific.     

Panoramic search: the interaction of memory and vision in search through a familiar scene

How do observers search through familiar scenes? A novel panoramic search method is used to study the interaction of memory and vision in natural search behavior. In panoramic search, observers see part of an unchanging scene larger than their current field of view. A target object can be visible, present in the display but hidden from view, or absent. Visual search efficiency does not change after hundreds of trials through an unchanging scene (Experiment 1). Memory search, in contrast, begins inefficiently but becomes efficient with practice. Given a choice between vision and memory, observers choose vision (Experiments 2 and 3). However, if forced to use their memory on some trials, they learn to use memory on all trials, even when reliable visual information remains available (Experiment 4). The results suggest that observers make a pragmatic choice between vision and memory, with a strong bias toward visual search even for memorized stimuli.     

Test-retest reliability of fMRI during nonverbal semantic decisions in moderate-severe nonfluent aphasia patients

Cortical reorganization in poststroke aphasia is not well understood. Few studies have investigated neural mechanisms underlying language recovery in severe aphasia patients, who are typically viewed as having a poor prognosis for language recovery. Although test-retest reliability is routinely demonstrated during collection of language data in single-subject aphasia research, this is rarely examined in fMRI studies investigating the underlying neural mechanisms in aphasia recovery. The purpose of this study was to acquire fMRI test-retest data examining semantic decisions both within and between two aphasia patients. Functional MRI was utilized to image individuals with chronic, moderate-severe nonfluent aphasia during nonverbal, yes/no button-box semantic judgments of iconic sentences presented in the Computer-assisted Visual Communication (C-ViC) program. We investigated the critical issue of intra-subject reliability by exploring similarities and differences in regions of activation during participants' performance of identical tasks twice on the same day. Each participant demonstrated high intra-subject reliability, with response decrements typical of task familiarity. Differences between participants included greater left hemisphere perilesional activation in the individual with better response to C-ViC training. This study provides fMRI reliability in chronic nonfluent aphasia, and adds to evidence supporting differences in individual cortical reorganization in aphasia recovery.     

Training-based interventions in motor rehabilitation after stroke: theoretical and clinical considerations

Basic neuroscience research on brain plasticity, motor learning and recovery has stimulated new concepts in neurological rehabilitation. Combined with the development of set methodological standards in clinical outcome research, these findings have led to a double-paradigm shift in motor rehabilitation: (a) the move towards evidence-based procedures for the assessment of clinical outcome & the employment of disablement models to anchor outcome parameters, and (b) the introduction of practice-based concepts that are derived from testable models that specify treatment mechanisms. In this context, constraint-induced movement therapy (CIT) has played a catalytic role in taking motor rehabilitation forward into the scientific arena. As a theoretically founded and hypothesis-driven intervention, CIT research focuses on two main issues. The first issue is the assessment of long-term clinical benefits in an increasing range of patient groups, and the second issue is the investigation of neuronal and behavioural treatment mechanisms and their interactive contribution to treatment success. These studies are mainly conducted in the research environment and will eventually lead to increased treatment benefits for patients in standard health care. However, gradual but presumably more immediate benefits for patients may be achieved by introducing and testing derivates of the CIT concept that are more compatible with current clinical practice. Here, we summarize the theoretical and empirical issues related to the translation of research-based CIT work into the clinical context of standard health care.     

The force of symmetry revisited: symmetry-to-noise ratios regulate (a)symmetry effects

Freyd and Tversky's [Am. J. Psychol. 97 (1984) 109] data suggested that human observers tend to overestimate relatively high levels of symmetry (symmetry effect), and tend to underestimate relatively low levels of symmetry (asymmetry effect). However, on the basis of their holographic approach to visual regularity, van der Helm and Leeuwenberg [Psychol. Rev. 103(3) (1996) 429] predicted that, at any level of symmetry, both symmetry and asymmetry effects may occur as a consequence of correct estimates of symmetry-to-noise ratios. This prediction was tested in two experiments, with tasks and stimuli similar to those in Freyd and Tversky's study. First, subjects had to judge whether a noisy symmetry is more similar to a slightly more symmetrical variant or to a slightly less symmetrical variant. Second, for every pair of stimuli in such a triadic comparison, subjects had to judge which stimulus is the more symmetrical one. The results from both experiments show that the occurrence of (a)symmetry effects indeed depends on symmetry-to-noise ratios.     

Minority adolescents and substance use risk/protective factors: a focus on inhalant use

Despite the fact that inhalant use is a growing problem among youth in the United States, relatively little attention has been paid to the demographic and social factors related to its use. This study used data from a household survey of adolescents in Washington state, and found that race/ethnicity was a strong predictor of lifetime prevalence of inhalant use, with Native-American youth being particularly likely to use inhalants. Comparing the age at initiation of inhalant use to other legal and illegal substances, we found that cigarettes and inhalants showed the lowest age at initiation. We conducted logistic regressions on lifetime prevalence of inhalant use, and compared these models to other substances. In general, we found that attachment to parents. parents' drug use, and school attachment were strong predictors of lifetime use of marijuana, alcohol, and inhalants. However, while peer drug use was a strong predictor of marijuana and alcohol use, it was not a significant predictor of adolescents' use of inhalants. Our final set of analyses included inhalant use in regression models predicting other problem behaviors: these analyses demonstrated that inhalant use was a strong predictor of involvement in problem behavior.     

Mental rotation depends on the number of objects rather than on the number of image fragments

It is often intuitively assumed that disconnected image fragments result in a representation of separate objects. When objects are partly occluded, disconnected image fragments can still result in a representation of a single object, based on visual completion. In a simultaneous matching task, displays showing one object, partly occluded objects, or two objects were compared with each other. When only a translation was required to match pairs of displays, one-object displays were matched faster than both occluded-object and two-object displays, which did not differ significantly from each other. When mental rotation and translation were required, the one-object displays were again matched the fastest. In addition, an advantage for occluded-object displays compared with two-object displays was found. We conclude that when the generation of a mental representation is likely, object-based connectedness determines object matching. Mental rotation then seems to depend on the number of objects rather than on the number of image fragments.     

Central inhibition ability modulates attention-induced motion blindness

Impaired motion perception can be induced in normal observers in a rapid serial visual presentation task. Essential for this effect is the presence of motion distractors prior to the motion target, and we proposed that this attention-induced motion blindness results from high-level inhibition produced by the distractors. To investigate this, we compared the extent of the attention-induced motion blindness effect with performance on central inhibition tasks: Stroop colour naming and negative priming. A negative correlation between Stroop interference and motion performance reflected that low Stroop scores, indicative of strong inhibition ability, was associated with more severe impairments in motion perception. This association could not be explained by individual differences in fluid intelligence, task switching or response speed. Negative priming was not specifically associated with attention-induced motion blindness. The results confirm that attention can modulate motion perception and suggest that the processes involved may be shared with high-level cognitive abilities.