Auditory temporal pattern learning in children with speech and language impairments

Four children demonstrating speech and language impairments were examined with respect to their ability to learn to identify certain auditory temporal perceptual information. These children listened to six-element temporal patterns and made judgments about the temporal proximity of two of the elements. Subjects listened to the patterns over a number of exposures ranging from 6 to 14, depending on the subject. Performance on the task improved significantly with repeated exposures. However, the disordered subjects' best performance was still significantly poorer than normal children who had only 1 exposure to the task. These results suggest that, in part, performance differences on temporal perceptual tasks between speech and language disordered children and normal children can be accounted for by differences in perceptual learning. However, because the disordered children never reached normal levels, learning differences may be associated with a fundamental deficit in temporal processing or some other mechanism such as impaired attention.     

A conditioned reinforcer maintained by temporal association with the termination of shock

Two experiments were conducted to determine whether a stimulus can be established as a positive conditioned reinforcer by associating it with the termination of shock, but without training the animal to make any response in its presence. In the first, six rats were conditioned to press a bar to terminate shock on a variable ratio schedule; white noise was then substituted as the immediate consequence, with the shock terminating 30 sec after the last press in its presence. It was found that the rate of pressing in the absence of noise depended on the contingency between the pressing and the noise. The second experiment sought to determine whether the difference in rates before and after the onset of the noise was due to the reinforcement of prior responding by the onset of the noise or to the suppression of subsequent responding by differential reinforcement of competing behavior. Six more rats were trained in the same manner, but with shock terminating 30 sec after the onset of the noise, regardless of what the animal did in its presence. Again the rate was higher before the onset of the noise, indicating that pressing was indeed maintained by the noise as a conditioned reinforcer.     

Scalar timing in temporal generalization in children with short and long stimulus durations.

This experiment investigated temporal generalization performance in children aged 3, 5, and 8 years by using auditory stimulus durations where the standard was 0.4 s or 4.0 s, and non-standard stimuli were spaced linearly around the standard. At all ages, generalization gradients superimposed well when plotted on the same relative scale, indicating conformity to scalar timing. Whatever the standard duration used, the principal developmental changes were the increasing steepness of the generalization gradient with increasing age and a shift from symmetrical gradients, in the 3- and 5-year-olds, to adult-like asymmetrical gradients in the 8-year-olds.     

Evidence for perceptual learning with repeated stimulation after partial and total cortical blindness

Lesions of occipital cortex result in loss of sight in the corresponding regions of visual fields. The traditional view that, apart from some spontaneous recovery in the acute phase, field defects remain permanently and irreversibly blind, has been challenged. In patients with partial field loss, a range of residual visual abilities in the absence of conscious perception (blindsight) has been demonstrated (Weiskrantz, 1986). Recent findings (Sahraie et al., 2006, 2010) have also demonstrated increased visual sensitivity in the field defect following repeated stimulation. We aimed to extend these findings by systematically exploring whether repeated stimulation can also lead to increased visual sensitivity in two cases with total (bilateral) cortical blindness. In addition, for a case of partial blindness, we examined the extent of the recovery as a function of stimulated region of the visual field, over extended periods of visual training. Positive auditory feedback was provided during the training task for correct detection of a spatial grating pattern presented at specific retinotopic locations using a temporal two alternative forced-choice paradigm (Neuro-Eye Therapy). All three cases showed improved visual sensitivity with repeated stimulation. The findings indicate that perceptual learning can occur through systematic visual field stimulation even in cases of bilateral cortical blindness.     

Habit and skill learning in schizophrenia: evidence of normal striatal processing with abnormal cortical input

Different forms of nondeclarative learning involve regionally specific striatal circuits. The motor circuit (involving the putamen) has been associated with motor–skill learning and the dorsolateral prefrontal cortex (DLPFC) circuit (involving the caudate) has been associated with cognitive–habit learning. Efforts to differentiate functional striatal circuits within patient samples have been limited. Previous studies have provided mixed results regarding striatal-dependent nondeclarative learning deficits in patients with schizophrenia. In this study, a cognitive–habit learning task (probabilistic weather prediction) was used to assess the DLPFC circuit and a motor–skill learning task (pursuit rotor) was used to assess the motor circuit in 35 patients with schizophrenia and 35 normal controls. Patients with schizophrenia displayed significant performance differences from controls on both nondeclarative tasks; however, cognitive–habit learning rate in patients did not differ from controls. There were performance and learning-rate differences on the motor–skill learning task between the whole sample of patients and controls, however, analysis of a subset of patients and controls matched on general intellectual level eliminated learning rate differences between groups. The abnormal performance offset between patients with schizophrenia and controls in the absence of learning rate differences suggests that abnormal cortical processing provides altered input to normal striatal circuitry.     

Evidence for distinct clusters of diverse anomalous experiences and their selective association with signs of elevated cortical hyperexcitability

Visual cortical hyperexcitability is now known to be an underlying factor for aberrant visual experience, including hallucinations, and pattern or light induced visual discomfort. Such factors have also been observed in neurological and non-clinical groups (albeit in attenuated form) – consistent with the notion of a continuum of anomalous experiences. Utilizing an exploratory factor analysis (EFA) approach (n = 300), Study 1 developed a revised proxy screening measure for visual cortical hyperexcitability – the Cortical Hyperexcitability index – II(CHi-II). The EFA revealed a stable 3-factor solution which can be characterised as; (i) Heightened Visual Sensitivity and Discomfort (HVSD); (ii) Aura-like Hallucinatory Experience (AHE); and, (iii) Distorted Visual Perception (DVP). Study 2 tested both a self-reported migraine group and a control group on the CHi-II in conjunction with a computerised pattern-glare task that is known to reflect visual cortical hyperexcitability. The migraine group produced significantly elevated scores on both the AHE and HVSD factors of the CHi-II, relative to controls. Among the non-migraine group, subjects who scored higher in the pattern-glare task also produced significantly elevated scores on the AHE factor compared to those with low pattern-glare task scores. Collectively, these findings support the utility of the CHi-II as an indirect proxy measure for signs of cortical hyperexcitability and reveal new categorical distinctions for the nature of the anomalous perceptions. These perceptions may well reflect diverse neurocognitive underpinnings leading to advancements in our understanding of aberrations in conscious experience.     

On the association of field dependence-independence with personality, learning style, and social-political attitudes among adolescents

This study examined the relationship between scores on field dependence and field independence and sensory learning preference, cognitive learning style, personality, interpersonal trust, attributions of responsibility for solving social problems, and attitudes regarding citizenship among youth. Participants were 72 private school students in Grades 6 through 12 (26 girls, 46 boys; M age: 15.2 yr., SD=1.9). When controlling for grade and sex, field independence (measured by Group Embedded Figures Test scores) was associated with Intuitive Thinking personality, Concrete lobal learning style, and rejection of individual responsibility for social problems, relative to governmental and community responsibility. Associations with other aspects of learning style fell short of significance. No association was found with generalized trust or citizenship attitudes. Reassessment of these variables with a larger sample should be undertaken.     

Morphological changes in dendritic spines of Purkinje cells associated with motor learning

Experience-dependent changes of spine structure and number may contribute to long-term memory storage. Although several studies demonstrated structural spine plasticity following associative learning, there is limited evidence associating motor learning with alteration of spine morphology. Here, we investigated this issue in the cerebellar Purkinje cells using high voltage electron microscopy (HVEM). Adult rats were trained in an obstacle course, demanding significant motor coordination to complete. Control animals either traversed an obstacle-free runway or remained sedentary. Quantitative analysis of spine morphology showed that the density and length of dendritic spines along the distal dendrites of Purkinje cells were significantly increased in the rats that learned complex motor skills compared to active or inactive controls. Classification of spines into shape categories indicated that the increased spine density and length after motor learning was mainly attributable to an increase in thin spines. These findings suggest that motor learning induces structural spine plasticity in the cerebellar Purkinje neurons, which may play a crucial role in acquiring complex motor skills.     

Transverse patterning reveals a dissociation of simple and configural association learning abilities in rats with 192 IgG-saporin lesions of the nucleus basalis magnocellularis

This experiment tests the hypothesis that the cholinergic nucleus basalis magnocellularis (NBM) is necessary for complex or configural association learning, but not elemental or simple association learning. Male Long-Evans rats with bilateral 192 IgG-saporin lesions of the NBM (n = 12) and sham-operated controls (n = 8) were tested in the transverse patterning problem, which provides a test of both simple and configural association learning. Rats were trained in phases to concurrently solve first one, then two, and finally three different visual discriminations; Problem 1 (A+ vs B- sign) and Problem 2 (B+ vs C-) could be solved using simple associations, whereas solving Problem 3 (C+ vs A-) required the ability to form configural associations. Consistent with our hypothesis, the NBM lesion group solved the simple discriminations in Problems 1 and 2 but showed impaired configural association learning in Problem 3. Additionally, when Problem 2 was introduced, previously high levels of performance on Problem 1 suffered more in the NBM lesion group than in the control group; this finding suggests an impairment in the ability of animals with NBM lesions to divide attention among multiple stimuli or to shift between strategies for solving different problems. Results support our argument that the NBM is critically involved in the acquisition of associative problems requiring a configural solution but not in problems that can be solved using only simple associations. The observed impairments in configural association learning and the apparent loss of cognitive flexibility or capacity are interpreted as reflecting specific attentional impairments resulting from NBM damage.     

Activation and survival of immature neurons in the dentate gyrus with spatial memory is dependent on time of exposure to spatial learning and age of cells at examination

Neurogenesis continues to occur throughout life in the dentate gyrus of the hippocampus and may be related to hippocampus-dependent learning. We have recently reported that there is an enhancement of neurogenesis in the hippocampus only when BrdU is administered 6 days prior to starting spatial training but not when training started either 1 day or 11 days following BrdU administration. In that study, all rats were perfused on day 16 after BrdU injection in order to compare cells of the same age (i.e. 16 day old cells) and thus the survival time after learning was different between groups. This study was designed to address whether the amount of time that passed following training could also contribute to the effects of spatial learning on hippocampal neurogenesis and whether there was differential new neuron activation in response to spatial learning that depended on the age of new cells at the time of spatial learning. Here we tested whether a survival period of 5 days following spatial learning at either 1-5, 6-10 or 11-15 days following BrdU administration would alter cell survival and/or activation of new neurons. Our results indicate that 5 days after training in the Morris water task cell survival is unaltered by training on days 1-5, increased by training at days 6-10 and decreased when training occurs on days 11-15. Furthermore spatial learners trained on days 6-10 or 11-15 show greater activation of new neurons compared to cue-trained rats during a probe trial 5 days after training. In addition, rats trained on the spatial task on days 11-15 had a greater number of activated new neurons compared to rats trained on the spatial task on days 6-10. These results suggest there is a gradual removal of older BrdU-labeled new neurons following spatial learning perhaps due to a competitive interaction with a population of younger BrdU-labeled new neurons.