Similarity and discrimination: A selective review and a connectionist model.

The 1st part of this article evaluates the extent to which 2 elemental theories of conditioning, stimulus sampling theory and the R. A. Rescorla-A. R. Wagner (1972) theory, are able to account for the influence of similarity on discrimination learning. A number of findings are reviewed that are inconsistent with predictions derived from these theories, either in their present form or in various modified forms. The 2nd part of the article is concerned with developing an alternative, configural account for discrimination learning. In contrast to previous configural theories, the present version is set within the framework of a connectionist network. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple-interval timing in rats: Performance on two-valued mixed fixed-interval schedules.

Three experiments studied timing in rats on 2-valued mixed-fixed-interval schedules, with equally probable components, Fixed-Interval S and Fixed-Interval L (FI S and FI L, respectively). When the L:S ratio was greater than 4, 2 distinct response peaks appeared close to FI S and FI L, and data could be well fitted by the sum of 2 Gaussian curves. When the L:S ratio was less than 4, only 1 response peak was usually visible, but nonlinear regression often identified separate sources of behavioral control, by FI S and FI L, although control by FI L dominated. Data were used to test ideas derived from scalar expectancy theory, the behavioral theory of timing, and learning to time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Word recall in schizophrenia: a connectionist model

OBJECTIVE: The authors examined word recall of patients with schizophrenia by using an experimental paradigm generated from connectionist models of memory. METHOD: Schizophrenic patients and normal comparison subjects first studied and then recalled a list of 32 words of equal difficulty. Both the connectivity (associative strength) and the network size (number of associates) of the words varied in such a way that the list contained equal proportions of four types of words: 1) high connectivity-small network size, 2) low connectivity-small network size, 3) high connectivity-large network size, and 4) low connectivity-large network size. RESULTS: The schizophrenic patients recalled fewer words and showed a particularly pronounced effect of the connectivity of the to-be-remembered words. For the patients, regardless of network size, recall improved substantially for words of high connectivity and declined dramatically for words of low connectivity. By contrast, the comparison subjects showed the expected effects, with the best recall for words of high connectivity-small network size, followed by words of low connectivity-small network size, then by words of high connectivity-large network size, and finally by words of low connectivity-large network size. CONCLUSIONS: Schizophrenia may be characterized by faulty modulation of associative links within a putative lexicon that is thought to be widely distributed across frontal and temporal lobes.     

ALCOVE: An exemplar-based connectionist model of category learning.

ALCOVE (attention learning covering map) is a connectionist model of category learning that incorporates an exemplar-based representation (D. L. Medin and M. M. Schaffer, 1978; R. M. Nosofsky, 1986) with error-driven learning (M. A. Gluck and G. H. Bower, 1988; D. E. Rumelhart et al, 1986). ALCOVE selectively attends to relevant stimulus dimensions, is sensitive to correlated dimensions, can account for a form of base-rate neglect, does not suffer catastrophic forgetting, and can exhibit 3-stage (U-shaped) learning of high-frequency exceptions to rules, whereas such effects are not easily accounted for by models using other combinations of representation and learning method. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of lesions of the ascending 5-hydroxytryptaminergic pathways on timing behaviour investigated with the fixed-interval peak procedure

Twelve rats received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei; 12 rats received sham lesions. The rats were then trained for 60 sessions under a discrete-trials fixed-interval schedule (peak procedure). In half the trials, a reinforcer became available 40 s after trial onset, and the trial was terminated upon reinforcer delivery; the remaining trials were 120 s in duration, and reinforcement did not occur in these trials. Performance during the 120-s trials was characterized by increasing response rate during the first 40 s of the trial, declining response rate between 40 s and 80 s, and a secondary increase in response rate during the final 40 s of the trial. The lesioned group showed a broader "spread" of the response rate function than the control group (time between attainment of 70% of the peak response rate and subsequent decline of response rate below this level); however, the peak response rate and the time from trial onset until attainment of the peak response rate did not differ significantly between the groups; the spread/peak-time ratio was significantly greater in the lesioned group than in the control group. The levels of 5-hydroxytryptamine (5HT) and 5-hydroxyindoleacetic acid in the parietal cortex, hippocampus, amygdala, nucleus accumbens and hypothalamus were markedly reduced in the lesioned group, but the levels of noradrenaline and dopamine were not significantly affected by the lesion. The results confirm the involvement of 5HTergic function in timing behaviour.     

A recurrent connectionist model of group biases.

Major biases and stereotypes in group judgments are reviewed and modeled from a recurrent connectionist perspective. These biases are in the areas of group impression formation (illusory correlation), group differentiation (accentuation), stereotype change (dispersed vs. concentrated distribution of inconsistent information), and group homogeneity. All these phenomena are illustrated with well-known experiments, and simulated with an autoassociative network architecture with linear activation update and delta learning algorithm for adjusting the connection weights. All the biases were successfully reproduced in the simulations. The discussion centers on how the particular simulation specifications compare with other models of group biases and how they may be used to develop novel hypotheses for testing the connectionist modeling approach and, more generally, for improving theorizing in the field of social biases and stereotype change. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesioning a connectionist model of visual search: Selective effects on distractor grouping.

Presents a connectionist model of visual search, Search via Recursive Rejection (SERR) by G. W. Humphreys and H. J. Muller (in press), in which search is determined by patterns of grouping between distractors and between simple form elements. The performance of SERR is examined after it is subject to various types of "lesion." Lesioning is produced either by increasing the internal noise on the activation functions governing the interactions between processing units or by eliminating processing units from different loci in SERR. Simulations demonstrate that (1) search processes can be disrupted by adding internal noise to search functions, (2) there can be selective effects on grouping processes, and (3) these selective effects can be associated with different types of lesion to different stages in SERR. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A connectionist model of complacency and adaptive recovery under automation.

Automation is intended to reduce the demands on operators in complex environments, thereby enhancing overall system performance. Although automation usually reduces workload, it is often accompanied by a decline in monitoring performance, an effect known as complacency. The circumstances under which complacency occurs and how it can be prevented, for example by intermittently returning control to the operator, are empirically well understood. To date, that empirical knowledge has not been accompanied by strong psychological theory. This article presents a computational model of human performance under automation based on connectionist principles. The model is shown to explain several benchmark findings, among them the basic complacency effect; the effect of the variability of automation reliability on complacency; the effect of task complexity; and the effect of intermittently returning control to the operator. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A connectionist model of septohippocampal dynamics during conditioning: Closing the loop.

Septohippocampal interactions determine how stimuli are encoded during conditioning. This study extends a previous neurocomputational model of corticohippocampal processing to incorporate hippocamposeptal feedback and examines how the presence or absence of such feedback affects learning in the model. The effects of septal modulation in conditioning were simulated by dynamically adjusting the hippocampal learning rate on the basis of how well the hippocampal system encoded stimuli. The model successfully accounts for changes in behavior and septohippocampal activity observed in studies of the acquisition, retention, and generalization of conditioned responses and accounts for the effects of septal disruption on conditioning. The model provides a computational, neurally based synthesis of prior learning theories that predicts changes in medial septal activity based on the novelty of stimulus events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Internal clock and memory processes in animal timing.

Two experiments, involving a total of 6 male pigeons, investigated temporal control of behavior within the framework of an internal clock model. Ss were exposed to signaled fixed interval (FI) 30-sec trials mixed with extended unreinforced (baseline) trials. On unreinforced break trials, the signal was interrupted for a period of time after trial onset. In Exp 1, comparisons between the peak time obtained on baseline and on break trials produced peak time shifts that were longer than those expected if the clock had stopped during the break but shorter than if the clock had reset. In Exp 2, systematic manipulations of duration and location of breaks produced peak time shifts that were nonlinear functions of break duration and that varied linearly with break location. The obtained peak times were more consistent with a continuous memory decay model than with the stop-retain or the reset hypotheses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The perching response and the laws of animal timing.

Homing pigeons were trained under differential-reinforcement-of-low-rate (DRL) or differential-reinforcement-of-response-duration (DRRD) schedules using a perching response. Schedule values ranged from 10 s to 70 s for DRL and from 12 s to 40 s for DRRD. In general, mean interresponse times or response durations were very close to the schedule requirement at all schedule values. A linear relation between mean response measure and schedule value described the data well, but power functions fared even better. The data also conformed well to the generalized Weber law; standard deviations of response measures varied as a linear function of the mean. Overall, the perching response produced data that conformed much more accurately to the schedule requirement—particularly at the longer schedule values—than did data from previous studies with both rats and pigeons. The results conformed well to the linear-type timing consistent with scalar timing theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"Lesioning a connectionist model of visual search: Selective effects on distractor grouping": Erratum.

Reports an error in the original article by G. W. Humphreys et al (Canadian Journal of Psychology, 1992, Vol 46, 417–460). The figures in the article were printed in the wrong order. Figures 2 and 6 should be interchanged, as should Figures 3 and 5. (The following abstract of this article originally appeared in record 1993-24303-001.) Presents a connectionist model of visual search, Search via Recursive Rejection (SERR) by G. W. Humphreys and H. J. Muller (in press), in which search is determined by patterns of grouping between distractors and between simple form elements. The performance of SERR is examined after it is subject to various types of "lesion.' Lesioning is produced either by increasing the internal noise on the activation functions governing the interactions between processing units or by eliminating processing units from different loci in SERR. Simulations demonstrate that (1) search processes can be disrupted by adding internal noise to search functions, (2) there can be selective effects on grouping processes, and (3) these selective effects can be associated with different types of lesion to different stages in SERR. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of similarity and experience on discrimination learning: A nonassociative connectionist model of perceptual learning.

This article describes a novel connectionist model of perceptual learning (PL) that provides a mechanism for nonassociative differentiation (J. J. Gibson & E. J. Gibson, 1955). The model begins with the assumption that 2 processes—1 that decreases associability and 1 that increases discriminability—operate during preexposure (S. Channell & G. Hall, 1981). In contrast to other models (e.g., I. P. L. McLaren, H. Kaye, & N. J. Mackintosh, 1989), in the current model the mechanisms for these processes are compatible with a configural model of associative learning. A set of simulations demonstrates that the present model can account for critical PL phenomena such as exposure learning and effects of similarity on discrimination. It is also shown that the model can explain the paradoxical result that preexposure to stimuli can either facilitate or impair subsequent discrimination learning. Predictions made by the model are discussed in relation to extant theories of PL. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Peak performance in sport: Identifying ideal performance states and developing athletes' psychological skills.

Can psychologists help performers in sport, business, and the performing arts achieve peak performances more often and with greater consistency? Sport psychologists have taken the lead in researching peak performance in an attempt to answer this question. This article focuses on optimal experiences in sport and ways in which the author works with athletes to help them achieve peak performances. Peak performance in sport is overviewed, the application of two models related to the preparation for peak performance in sport are discussed, and applied sport psychology experiential knowledge is shared. Implications for practice for psychologists considering work in this area are also considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Towards a neural model of timing

This paper describes a neural model of interval timing, which reproduces the duration discrimination experiments of Wearden, J.H., 1992, J. Exp. Psychol. 18, 134-144. The model comprises three layers of neural units. The units in the first layer represent clusters of neurons with probabilistic internal feedback that maintains self-sustained (short-term memory) activity for a random time. The unit in the second layer is a spiking neuron that fires as long as a sufficient number of input clusters are active. The unit in the third layer detects the offset of firing in the previous layer by producing a short burst of spikes. Analysis and simulation of the model shows spikes produced at random times with a distribution determined by the number of units in the first layer, their survival time constant, and the threshold of the unit in layer 2. Interval times can be learned with any of these parameters but lead to different Weber law relations. A variable threshold in layer 2 predicts S-shaped Weber curves, a variable number of units in layer 1 leads to a saturation of the Weber curve (decreasing Weber fraction) and a variable time constant in layer 1 causes a linear Weber curve.     

Mathematical and connectionist models of human memory: a comparison

Recent convolution-based models of human memory (e.g. Lewandowsky & Murdock, 1989), have accounted for a wide range of data. However such models require the relevant mathematical operations to be provided to the network. Connectionist models, in contrast, have generally addressed different data, and not all architectures are appropriate for modelling single-trial learning. Furthermore, they tend to exhibit catastrophic interference in multiple list learning. In this paper we compare the ability of convolution-based models and DARNET (Developmental Associative Recall NETwork), to account for human memory data. DARNET is a connectionist approach to human memory in which the system gradually learns to associate vectors, in one trial, into a memory trace vector. Either of the vectors can than be retrieved. It is shown that the new associative mechanism can be used to account for a wide range of relevant experimental data as successfully as can convolution-based models with the same higher-level architectures. Limitations of the models are also addressed.     

Memory variance in the peak procedure of timing in pigeons.

Pigeons were rewarded on a fixed interval (FI) schedule. On occasional unrewarded tests, they usually showed a break–run–break pattern of responding. Across trials, the start of the run correlated positively with the end, suggesting variance across trials in (1) clock speed, (2) the delay to start the clock, or (3) a single criterion time used on a trial. If variance in criterion time exists, then a task in which the start and the end of the run are based on independent criterion times should produce a reduced start–end correlation. In 2 such tasks, the start–end correlation dropped to near zero, although other correlations were comparable to those found in the standard FI task. This provides evidence for variance across trials in a single criterion time used on a trial. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Causal explanation as constraint satisfaction: A critique and a feedforward connectionist alternative.

S. J. Read and A. Marcus-Newhall (1993) proposed that constraint satisfaction connectionist models can account for four principles of coherence that underlie social explanation. However, it is argued that the specific implementation they used (ECHO; R. Thagard, 1992) has several important shortcomings. ECHO fails to be sensitive to covariation that is crucial to causality, it does not learn from experience, and it cannot deal efficiently with conjunctions of explanations. To remedy these shortcomings, the author presents an alternative feedforward connectionist model that prior research has shown to be susceptible to the classical attribution principles of covariation, discounting, and augmentation. By running novel simulations of Read and Marcus-Newhall's data, the author demonstrated that this feedforward model is also capable of simulating the four principles of coherence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Self-handicapping and defensive pessimism: Exploring a model of predictors and outcomes from a self-protection perspective.

The present study is centrally concerned with self-handicapping and defensive pessimism (comprising defensive expectations and reflectivity), the factors that predict these strategies, and the associations between these strategies and a variety of academic outcomes. Major findings are that task orientation negatively predicts both self-handicapping and defensive expectations and positively predicts reflectivity; uncertain personal control positively predicts defensive expectations, and to a lesser extent, self-handicapping; and an external attributional orientation is positively associated with self-handicapping, and to a lesser extent, defensive expectations. Both self-handicapping and defensive expectations are negatively associated with self-regulation and persistence, whereas reflectivity is positively associated with these outcomes. Students high in self-handicapping received lower end-of-year grades than did students low in self-handicapping and were less likely to be in attendance 1 year later. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exploring a model of intuitive eating with college women.

Intuitive eating (i.e., eating based on physiological hunger and satiety cues rather than situational and emotional cues) recently has gained recognition as an adaptive eating style. The present study explored a model of intuitive eating based on a foundation of acceptance with 2 samples of college women. Path analysis with the 1st sample (N = 181) revealed that the acceptance model provided an excellent fit to the data, and latent variable structural equation modeling with the 2nd sample (N = 416) cross-validated this model. Specifically, general unconditional acceptance predicted body acceptance by others, body acceptance by others predicted an emphasis on body function over appearance, body acceptance by others and an emphasis on body function predicted body appreciation, and an emphasis on body function and body appreciation predicted intuitive eating. (PsycINFO Database Record (c) 2010 APA, all rights reserved)