Modeling human sequence learning under incidental conditions.

This research explored the role that associative learning may play in human sequence learning. Two-choice serial reaction time tasks were performed under incidental conditions using 2 different sequences. In both cases, an experimental group was trained on 4 subsequences: LLL, LRL, RLR, and RRR for Group "Same" and LLR, LRR, RLL, and RRL for Group "Different," with left and right counterbalanced across participants. To control for sequential effects, we assayed sequence learning by comparing their performance with that of a control group, which had been trained on a pseudorandom ordering, during a test phase in which both experimental and control groups experienced the same subsequences. Participants in both groups showed sequence learning, but the group trained on "different" learned more and more rapidly. This result is the opposite that predicted by the augmented simple recurrent network used by F. W. Jones and I. P. L. McLaren (2009, Human sequence learning under incidental and intentional conditions, Journal of Experimental Psychology: Animal Behavior Processes, Vol. 35, pp. 538-553), but can be modeled using a reparameterized version of this network that also includes a more realistic representation of the stimulus array, suggesting that the latter may be a better model of human sequence learning under incidental conditions.

Syntactic transfer in artificial grammar learning.

In an artificial grammar learning (AGL) experiment, participants were trained with instances of one grammatical structure before completing a test phase in which they were required to discriminate grammatical from randomly created strings. Importantly, the underlying structure used to generate test strings was different from that used to generate the training strings. Despite the fact that grammatical training strings were more similar to nongrammatical test strings than they were to grammatical test strings, this manipulation resulted in a positive transfer effect, as compared with controls trained with nongrammatical strings. It is suggested that training with grammatical strings leads to an appreciation of set variance that aids the detection of grammatical test strings in AGL tasks. The analysis presented demonstrates that it is useful to conceptualize test performance in AGL as a form of unsupervised category learning.

A comparative analysis of the categorization of multidimensional stimuli: I. Unidimensional classification does not necessarily imply analytic processing; evidence from pigeons (Columba livia), squirrels (Sciurus carolinensis), and humans (Homo sapiens).

Pigeons (Columba livia), gray squirrels (Sciurus carolinensis), and undergraduates (Homo sapiens) learned discrimination tasks involving multiple mutually redundant dimensions. First, pigeons and undergraduates learned conditional discriminations between stimuli composed of three spatially separated dimensions, after first learning to discriminate the individual elements of the stimuli. When subsequently tested with stimuli in which one of the dimensions took an anomalous value, the majority of both species categorized test stimuli by their overall similarity to training stimuli. However some individuals of both species categorized them according to a single dimension. In a second set of experiments, squirrels, pigeons, and undergraduates learned go/no-go discriminations using multiple simultaneous presentations of stimuli composed of three spatially integrated, highly salient dimensions. The tendency to categorize test stimuli including anomalous dimension values unidimensionally was higher than in the first set of experiments and did not differ significantly between species. The authors conclude that unidimensional categorization of multidimensional stimuli is not diagnostic for analytic cognitive processing, and that any differences between human's and pigeons' behavior in such tasks are not due to special features of avian visual cognition.

Processes of overall similarity sorting in free classification.

The processes of overall similarity sorting were investigated in 5 free classification experiments. Experiments 1 and 2 demonstrated that increasing time pressure can reduce the likelihood of overall similarity categorization. Experiment 3 showed that a concurrent load also reduced overall similarity sorting. These findings suggest that overall similarity sorting can be a time-consuming analytic process. Such results appear contrary to the idea that overall similarity is a nonanalytic process (e.g., T. B. Ward, 1983) but are in line with F. N. Milton and A. J. Wills's (2004) dimensional summation hypothesis and with the stochastic sampling assumptions of the extended generalized context model (K. Lamberts, 2000). Experiments 4 and 5 demonstrated that the relationship between stimulus presentation time and overall similarity sorting is nonmonotonic, and the shape of the function is consistent with the idea that the three aforementioned processes operate over different parts of the time course.

Does maintenance of colour categories rely on language? Evidence to the contrary from a case of semantic dementia.

Recent neuropsychological evidence, supporting a strong version of Whorfian principles of linguistic relativity, has reinvigorated debate about the role of language in colour categorisation. This paper questions the methodology used in this research and uses a novel approach to examine the unique contribution of language to categorisation behaviour. Results of three investigations are reported. The first required development of objective measures of category coherence and consistency to clarify questions about healthy control performance on the freesorting colour categorisation task used in previous studies. Between-participant consistency was found to be only moderate and the number of colour categories generated was found to vary markedly between individuals. The second study involved longitudinal neuropsychological examination of a patient whose colour categorisation strategy was monitored in the context of a progressive decline in language due to semantic dementia. Performance on measures of category coherence and consistency was found to be relatively stable over time despite a profound decline in the patient's colour language. In a final investigation we demonstrated that, for both the patient and controls, between- and within-participant consistency were higher than expected by (a) random sorting and (b) sorting perceptually similar chips together. These findings indicate that the maintenance of colour categorisation need not depend on language.

Predictive learning, prediction errors, and attention: evidence from event-related potentials and eye tracking.

Prediction error ("surprise") affects the rate of learning: We learn more rapidly about cues for which we initially make incorrect predictions than cues for which our initial predictions are correct. The current studies employ electrophysiological measures to reveal early attentional differentiation of events that differ in their previous involvement in errors of predictive judgment. Error-related events attract more attention, as evidenced by features of event-related scalp potentials previously implicated in selective visual attention (selection negativity, augmented anterior N1). The earliest differences detected occurred around 120 msec after stimulus onset, and distributed source localization (LORETA) indicated that the inferior temporal regions were one source of the earliest differences. In addition, stimuli associated with the production of prediction errors show higher dwell times in an eye-tracking procedure. Our data support the view that early attentional processes play a role in human associative learning.

Respiratory involvement in inherited primary muscle conditions.

Patients with inherited muscle disorders can develop respiratory muscle weakness leading to ventilatory failure. Predicting the extent of respiratory involvement in the different types of inherited muscle disorders is important, as it allows clinicians to impart prognostic information and offers an opportunity for early interventional management strategies. The approach to respiratory assessment in patients with muscle disorders, the current knowledge of respiratory impairment in different muscle disorders and advice on the management of respiratory complications are summarised.

Formation of category representations.

Many formal models of categorization assume, implicitly or explicitly, that categorization results in the formation of direct associations from representations of the presented stimuli to representations of the experimentally provided category labels. In three categorization experiments employing a polymorphous classification structure (Dennis, Hampton, & Lea, 1973) and a partial reversal, optional shift procedure (Kendler, Kendler, & Wells, 1960), we provide evidence consistent with the hypothesis that learning a new classification problem results in the creation of category representations that mediate between representations of the stimulus and the label. This hypothesis can be instantiated through the AMBRY model (Kruschke, 1996).

Oculopharyngeal muscular dystrophy: a point mutation which mimics the effect of the PABPN1 gene triplet repeat expansion mutation.

BACKGROUND: Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant late onset neuromuscular disease characterised by proximal muscle weakness, ptosis, and swallowing difficulty. The only causative mutation described to date is a triplet repeat expansion consisting of two to seven additional base triplets in a repeat sequence in exon 1 of the polyadenine binding protein nuclear 1 (PABPN1) gene. This results in an increase in length of a polyalanine tract in the PABPN1 protein from 10 to 12-17 residues. OBJECTIVE: Description of another mutation in a case of OPMD. METHODS: Sequence analysis of exon 1 of the PABPN1 gene was undertaken on 202 patients referred for a possible diagnosis of OPMD but negative for the triplet repeat expansion mutation. RESULTS: A case was identified with typical symptoms of OPMD, negative for the repeat expansion mutation but with a missense mutation in PABPN1 close to the 3' end of the normal polyalanine codon repeat sequence. CONCLUSIONS: The single base mutation changes a glycine codon to an alanine codon and results in an increase in the number of contiguous polyalanine codons. This mimics the effect of the common triplet repeat expansion mutation and represents a previously undescribed mechanism of mutation.

Why are artificial polymorphous concepts so hard for birds to learn?

Stimulus sets defined in terms of artificial polymorphous concepts have frequently been used in experiments to investigate the mechanisms of discrimination of natural concepts, both in humans and in other animals. However, such stimulus sets are frequently difficult for either animals or humans to discriminate. Properties of artificial polymorphous stimulus sets that might explain this difficulty include the complexity of the individual stimuli, the unreliable reinforcement of individual positive features, attentional load, difficulties in discriminating some stimulus dimensions, memory load, and a lack of the correlation between features that characterizes natural concepts. An experiment using chickens as subjects and complex artificial visual stimulus sets investigated these hypotheses by training the birds in discriminations that were not polymorphous but did have some of the properties listed above. Discriminations that involved unreliable reinforcement or high attentional load were found to approach the difficulty of polymorphous concept discriminations, and these two factors together were sufficient to account for the entire difficulty. The usual kind of artificial polymorphous concept may not be a good model for natural concepts as they are perceived and discriminated by birds. A RULEX account of natural concept learning may be preferable.

Tubular aggregate myopathy presenting with acute type II respiratory failure and severe orthopnoea.

Acute hypercapnic respiratory failure (AHRF) is a common reason for hospital admission. Most patients have an underlying chronic lung disease such as chronic obstructive pulmonary disease. We report the case of a man who presented with AHRF secondary to tubular aggregate myopathy.

Ataxia, peripheral neuropathy, and anti-gliadin antibody. Guilt by association?

Some authors contend that patients with idiopathic neurological disease who are also anti-gliadin antibody seropositive are gluten sensitive. However, anti-gliadin antibodies lack disease specificity being found in 10% of healthy blood donors. We report a study comparing anti-gliadin antibody with other food antibodies in patients with idiopathic ataxia (20), hereditary ataxias (seven), or idiopathic peripheral neuropathy (32). Patients were HLA typed. IgA anti-tissue transglutaminase antibodies (tTG) were measured. No case was positive for IgA anti-tTG making occult coeliac disease unlikely. HLA DQ2 and HLA DQ8 were found distributed equally across all patient groups and unrelated to gliadin antibody status. HLA DQ2 expressing, anti-gliadin antibody positive cases (so called "gluten ataxia") were rare in our clinics (four cases in 2 years from a population of 2 million). We conclude that coeliac disease per se is not commonly associated with either idiopathic ataxia or idiopathic peripheral neuropathy. Our study also casts doubt on the nosological status of "gluten ataxia" as a discreet disease entity. All food antibodies tested, particularly IgG, were a common finding in both ataxia and peripheral neuropathy groups. No particular food antibody was associated with any patient group. Food antibodies were equally common in hereditary ataxias. We conclude they are a non-specific finding.

Thymectomy in myasthenia gravis: comparison of outcome in Santiago, Cuba and Nottingham, UK.

OBJECTIVES: We compared the outcome of thymectomy for myasthenia gravis (MG) in two healthcare systems. In Nottingham, UK, thymectomy is performed for thymic enlargement and considered in acetylcholine receptor (AchR) antibody positive patients. In Santiago, Cuba, thymectomy is considered in all generalised MG patients irrespective of their radiological findings or AchR antibodies. METHOD: 22 MG patients in Nottingham and 75 in Santiago who had a thymectomy were identified and their notes reviewed. We compared the median age, stage of disease, thymic histology and clinical outcome at two years post-thymectomy. RESULTS: The median ages for the Cuban and Nottingham patients were 25 and 35 years respectively. The median stage of disease was IIa by Osserman's classification in both. In Nottingham, 59% (13/22) showed an improvement compared with 88 % (66/75) in Santiago (p < 0.01). There were significantly more cases of thymoma in Nottingham whereas thymic hyperplasia and atrophy were a more frequent finding in Cuban patients. The majority of cases who improved post-thymectomy had thymic hyperplasia on histology in both Nottingham (46%) and Cuban (61%) patients. CONCLUSION: Selecting MG patients based on thymic enlargement alone or AchR antibody positivity may be inadequate and thymectomy should perhaps be considered in all patients with generalised myasthenia.

Thymectomy in myasthenia gravis: comparison of outcome in Santiago, Cuba and Nottingham, UK

OBJECTIVES: We compared the outcome of thymectomy for myasthenia gravis (MG) in two healthcare systems. In Nottingham, UK, thymectomy is performed for thymic enlargement and considered in acetylcholine receptor (AchR) antibody positive patients. In Santiago, Cuba, thymectomy is considered in all generalised MG patients irrespective of their radiological findings or AchR antibodies. METHOD: 22 MG patients in Nottingham and 75 in Santiago who had a thymectomy were identified and their notes reviewed. We compared the median age, stage of disease, thymic histology and clinical outcome at two years post-thymectomy. RESULTS: The median ages for the Cuban and Nottingham patients were 25 and 35 years respectively. The median stage of disease was IIa by Osserman's classification in both. In Nottingham, 59 percent (13/22) showed an improvement compared with 88 percent (66/75) in Santiago (p < 0.01). There were significantly more cases of thymoma in Nottingham whereas thymic hyperplasia and atrophy were a more frequent finding in Cuban patients. The majority of cases who improved post-thymectomy had thymic hyperplasia on histology in both Nottingham (46 percent) and Cuban (61 percent) patients. CONCLUSION: Selecting MG patients based on thymic enlargement alone or AchR antibody positivity may be inadequate and thymectomy should perhaps be considered in all patients with generalised myasthenia(AU)

Significance of Beevor's sign in facioscapulohumeral dystrophy and other neuromuscular diseases.

An atypical presentation of facioscapulohumeral dystrophy (FSH) is described, where the presence of a positive Beevor's sign led to genetic testing and subsequent probable diagnostic confirmation. This prompted evaluation of a further 68 patients for the presence of Beevor's sign. Among these, 19/20 patients with FSH had a positive Beevor's sign, compared with 2/28 with other muscle diseases, and 0/20 in a neurological control group. Beevor's sign should be considered as an additional criterion for the diagnosis of FSH.

The outcome specificity of learned predictiveness effects: parallels between human causal learning and animal conditioning.

Two experiments examined the outcome specificity of a learned predictiveness effect in human causal learning. Experiment 1 indicated that prior experience of a cue-outcome relation modulates learning about that cue with respect to a different outcome from the same affective class but not with respect to an outcome from a different affective class. Experiment 2 ruled out an interpretation of this effect in terms of context specificity. These results indicate that learned predictiveness effects in human causal learning index an associability that is specific to a particular class of outcomes. Moreover, they mirror demonstrations of the reinforcer specificity of analogous effects in animal conditioning, supporting the suggestion that, under some circumstances, human causal learning and animal conditioning reflect the operation of common associative mechanisms.

Global-feature classification can be acquired more rapidly than local-feature classification in both humans and pigeons.

When humans process visual stimuli, global information often takes precedence over local information. In contrast, some recent studies have pointed to a local precedence effect in both pigeons and nonhuman primates. In the experiment reported here, we compared the speed of acquisition of two different categorizations of the same four geometric figures. One categorization was on the basis of a local feature, the other on the basis of a readily apparent global feature. For both humans and pigeons, the global-feature categorization was acquired more rapidly. This result reinforces the conclusion that local information does not always take precedence over global information in nonhuman animals.