The Isolation, Primacy, and Recency Effects Predicted by an Adaptive LTD/LTP Threshold in Postsynaptic Cells

Building a unified model of the Optional Infinitive Stage: Simulating the cross-linguistic pattern of verb-marking error in typically developing children and children with Developmental Language Disorder

Verb-marking errors are a characteristic feature of the speech of typically-developing (TD) children and are particularly prevalent in the speech of children with Developmental Language Disorder (DLD). However, both the pattern of verb-marking error in TD children and the pattern of verb-marking deficit in DLD vary across languages and interact with the semantic and syntactic properties of the language being learned. In this paper, we review work using a computational model called MOSAIC. We show how this work allows us to understand several features of the cross-linguistic data that are otherwise difficult to explain. We also show how discrepancies between the developmental data and the quantitative predictions generated by MOSAIC can be used to identify weaknesses in our current understanding and lead to further theory development; and how the resulting model (MOSAIC+) helps us understand differences in the cross-linguistic patterning of verb-marking errors in TD children and children with DLD.

Examining resurgence in rats following expanded-operant treatments

Resurgence of previously reinforced behavior represents a challenge to otherwise successful interventions based on differential reinforcement of alternative behavior (DRA). Expanded-operant treatments seek to increase the number of functional alternative behaviors through DRA, thereby potentially mitigating resurgence. However, the few studies that have directly examined these methods as a tool for resurgence mitigation have provided limited and unclear results. Thus, the present experiments were designed to investigate the effect of expanded-operant DRA methods on resurgence of previously reinforced behavior using rat subjects. In two experiments, following a baseline phase in which a target response was trained, groups of rats experienced concurrent (i.e., five simultaneous alternative responses), serial (i.e., five sequentially available alternative responses), or single DRA interventions arranging similar rates of alternative reinforcement in order to examine potential differences in resurgence. Both experiments showed that neither serial nor concurrent DRA expanded-operant treatments reduced resurgence compared with single DRA regardless of whether stimuli associated with previously reinforced alternative responses were removed (Experiment 1) or remained present (Experiment 2) for the serial-DRA group. Further, a primacy effect in resurgence was obtained for the serial-DRA group in both experiments. Overall, these results suggest that expanded-operant treatments may not help to reduce resurgence.

Distinctiveness and priority in free recall of words

Participants recalled low- and high-priority words varying in distinctiveness in three experiments. Word priority was established by assigning point values based on font colour or conceptual category. Word distinctiveness varied across three list structures: homogeneous lists of words (same colour or category), 50/50 lists containing words in two font colours or from two categories, and isolation lists in which a word was isolated in serial position two either by colour (Experiments 1 and 2) or category (Experiment 3). Word priority was established before list presentation in Experiment 1 and after list presentation in Experiments 2 and 3. When colour priority was established before list presentation, participants recalled high-priority words better than low-priority words across all list structures. Early isolation enhanced recall for high-priority words but impaired recall for low-priority words. When colour priority was established after list presentation, neither priority nor distinctiveness enhanced recall. When category priority was established after list presentation, participants recalled high-priority words better than low-priority words, and isolation only enhanced recall when it was combined with high priority. We concluded that priority and distinctiveness combine to produce the early isolation effect, and that encoding and retrieval processes interact to enhance memory for high-priority and distinctive events.

Representation of Rapid Image Sequences in V4 Networks

Natural viewing often consists of sequences of brief fixations to image patches of different structure. Whether and how briefly presented sequential stimuli are encoded in a temporal-position manner is poorly understood. Here, we performed multiple-electrode recordings in the visual cortex (area V4) of nonhuman primates (Macaca mulatta) viewing a sequence of 7 briefly flashed natural images, and measured correlations between the cue-triggered population response in the presence and absence of the stimulus. Surprisingly, we found significant correlations for images occurring at the beginning and the end of a sequence, but not for those in the middle. The correlation strength increased with stimulus exposure and favored the image position in the sequence rather than image identity. These results challenge the commonly held view that images are represented in visual cortex exclusively based on their informational content, and indicate that, in the absence of sensory information, neuronal populations exhibit reactivation of stimulus-evoked responses in a way that reflects temporal position within a stimulus sequence.

ENDOWMENT EFFECT AND HOUSING DECISIONS

Endowment effect refers to the reported gaps between willingness to accept and willingness to pay. According to prospect theory, this effect is a result of the underweighting of opportunity costs. Given the high stake involved in a typical housing transaction, endowment effect is expected to have a significant influence on housing decisions. We develop a theoretical framework to study the presence of endowment effect and its role in housing decision-making process. Three hypotheses are derived and tested through a field experiment conducted in Beijing, China. Our empirical results show that endowment effect plays an important role in the formation of judgmental biases in housing decisions. Moreover, endowment effect interacts with housing cycles. Our study highlights the application of prospect theory in the housing market; thus, it not only extends existing theoretical and empirical works in this important sector, but also clarifies consumer behavior in the emerging property market of China.

Reactivation in working memory: an attractor network model of free recall

The dynamic nature of human working memory, the general-purpose system for processing continuous input, while keeping no longer externally available information active in the background, is well captured in immediate free recall of supraspan word-lists. Free recall tasks produce several benchmark memory phenomena, like the U-shaped serial position curve, reflecting enhanced memory for early and late list items. To account for empirical data, including primacy and recency as well as contiguity effects, we propose here a neurobiologically based neural network model that unifies short- and long-term forms of memory and challenges both the standard view of working memory as persistent activity and dual-store accounts of free recall. Rapidly expressed and volatile synaptic plasticity, modulated intrinsic excitability, and spike-frequency adaptation are suggested as key cellular mechanisms underlying working memory encoding, reactivation and recall. Recent findings on the synaptic and molecular mechanisms behind early LTP and on spiking activity during delayed-match-to-sample tasks support this view.

Neuroelectric evidence for cognitive association formation: an event-related potential investigation

Although many types of learning require associations to be formed, little is known about the brain mechanisms engaged in association formation. In the present study, we measured event-related potentials (ERPs) while participants studied pairs of semantically related words, with each word of a pair presented sequentially. To narrow in on the associative component of the signal, the ERP difference between the first and second words of a pair (Word2-Word1) was derived separately for subsequently recalled and subsequently not-recalled pairs. When the resulting difference waveforms were contrasted, a parietal positivity was observed for subsequently recalled pairs around 460 ms after the word presentation onset, followed by a positive slow wave that lasted until around 845 ms. Together these results suggest that associations formed between semantically related words are correlated with a specific neural signature that is reflected in scalp recordings over the parietal region.