Richard L. Lewis

Computational principles of working memory in sentence comprehension

Understanding a sentence requires a working memory of the partial products of comprehension, so that linguistic relations between temporally distal parts of the sentence can be rapidly computed. We describe an emerging theoretical framework for this working memory system that incorporates several independently motivated principles of memory: a sharply limited attentional focus, rapid retrieval of item (but not order) information subject to interference from similar items, and activation decay (forgetting over time). A computational model embodying these principles provides an explanation of the functional capacities and severe limitations of human processing, as well as accounts of reading times. The broad implication is that the detailed nature of cross-linguistic sentence processing emerges from the interaction of general principles of human memory with the specialized task of language comprehension.

Interference in Short-Term Memory: The Magical Number Two (or Three) in Sentence Processing

Many theories have been proposed to explain difficulty with center embedded constructions, most attributing the problem to some kind of limited-capacity short-term memory. However, these theories have developed for the most part independently of more traditional memory research, which has focused on uncovering general principles such as chunking and interference. This article attempts to gain some unification with this research by suggesting that an interesting range of core sentence processing phenomena can be explained as interference effects in a sharply limited syntactic working memory. These include difficult and acceptable embeddings, as well as certain limitations on ambiguity resolution, length effects in garden path structures, and the requirement for locality in syntactic structure. The theory takes the form of an architecture for parsing that can index no more than two constituents under the same syntactic relation. A limitation of two or three items shows up in a variety of other verbal short-term memory tasks as well.

Intrinsically Motivated Reinforcement Learning: An Evolutionary Perspective

There is great interest in building intrinsic motivation into artificial systems using the reinforcement learning framework. Yet, what intrinsic motivation may mean computationally, and how it may differ from extrinsic motivation, remains a murky and controversial subject. In this paper, we adopt an evolutionary perspective and define a new optimal reward framework that captures the pressure to design good primary reward functions that lead to evolutionary success across environments. The results of two computational experiments show that optimal primary reward signals may yield both emergent intrinsic and extrinsic motivation. The evolutionary perspective and the associated optimal reward framework thus lead to the conclusion that there are no hard and fast features distinguishing intrinsic and extrinsic reward computationally. Rather, the directness of the relationship between rewarding behavior and evolutionary success varies along a continuum.

Distinguishing effects of structure and decay on attachment and repair: A cue-based parsing account of recovery from misanalyzed ambiguities

This paper presents the cue-based retrieval theory of parsing and reanalysis and illustrates how this account can accommodate a number of key results about parsing and reanalysis, including effects due to structure, distance, and type of structural change. Three offline experiments and one online experiment permit establishing the locus of these effects as due to properties of the initial parsing processes or to the repair mechanism. Specifically, the data reported here suggest that a structural factor specific to the operation of the parser, retrieval interference, affects attachment uniformly across ambiguous and unambiguous sentences and serves to create a limit on successful repair. In addition, these experiments suggest that distance of the head of an ambiguous phrase from its disambiguator affects repair processes—and not attachment processes—independently of the interference effect. These results are interpreted with respect to alternative models of reanalysis, which are contrasted with the cue-based retrieval account, which requires no distinct repair mechanism to account for the current results. A further contribution of this article is to suggest a statistical correction for individual variance in reading rates. Statistical analyses on individual subject data confirmed previous speculations regarding a possible increase in reading rates as subjects move through a sentence. While this individual variation limits fair comparisons of reading times in sentence regions that appear in non-identical serial positions, we demonstrate that such comparisons become meaningful when the appropriate regression analyses have been performed.

Rational adaptation under task and processing constraints: Implications for testing theories of cognition and action

The authors assume that individuals adapt rationally to a utility function given constraints imposed by their cognitive architecture and the local task environment. This assumption underlies a new approach to modeling and understanding cognition-cognitively bounded rational analysis-that sharpens the predictive acuity of general, integrated theories of cognition and action. Such theories provide the necessary computational means to explain the flexible nature of human behavior but in doing so introduce extreme degrees of freedom in accounting for data. The new approach narrows the space of predicted behaviors through analysis of the payoff achieved by alternative strategies, rather than through fitting strategies and theoretical parameters to data. It extends and complements established approaches, including computational cognitive architectures, rational analysis, optimal motor control, bounded rationality, and signal detection theory. The authors illustrate the approach with a reanalysis of an existing account of psychological refractory period (PRP) dual-task performance and the development and analysis of a new theory of ordered dual-task responses. These analyses yield several novel results, including a new understanding of the role of strategic variation in existing accounts of PRP and the first predictive, quantitative account showing how the details of ordered dual-task phenomena emerge from the rational control of a cognitive system subject to the combined constraints of internal variance, motor interference, and a response selection bottleneck.

In Search of Decay in Verbal Short-Term Memory.

Is forgetting in the short term due to decay with the mere passage of time, interference from other memoranda, or both? Past research on short-term memory has revealed some evidence for decay and a plethora of evidence showing that short-term memory is worsened by interference. However, none of these studies has directly contrasted decay and interference in short-term memory in a task that rules out the use of rehearsal processes. In this article the authors present a series of studies using a novel paradigm to address this problem directly, by interrogating the operation of decay and interference in short-term memory without rehearsal confounds. The results of these studies indicate that short-term memories are subject to very small decay effects with the mere passage of time but that interference plays a much larger role in their degradation. The authors discuss the implications of these results for existing models of memory decay and interference.

A computational unification of cognitive behavior and emotion

Existing models that integrate emotion and cognition generally do not fully specify why cognition needs emotion and conversely why emotion needs cognition. In this paper, we present a unified computational model that combines an abstract cognitive theory of behavior control (PEACTIDM) and a detailed theory of emotion (based on an appraisal theory), integrated in a theory of cognitive architecture (Soar). The theory of cognitive control specifies a set of required computational functions and their abstract inputs and outputs, while the appraisal theory specifies in more detail the nature of these inputs and outputs and an ontology for their representation. We argue that there is a surprising functional symbiosis between these two independently motivated theories that leads to a deeper theoretical integration than has been previously obtained in other computational treatments of cognition and emotion. We use an implemented model in Soar to test the feasibility of the resulting integrated theory, and explore its implications and predictive power in several task domains.

Divergent effects of different positive emotions on moral judgment

Positive emotions are often treated as relatively similar in their cognitive-behavioral effects, and as having unambiguously beneficial consequences. For example, Valdesolo and DeSteno (2006) reported that a humorous video made people more prone to choose a utilitarian solution to a moral dilemma. They attributed this finding to increased positive affect. To determine whether such results actually stem in general from positive affect or from other more specific properties of humor, we conducted an experiment with moral dilemmas presented during an interleaved emotion-induction procedure involving mirth and another positive emotion, elevation. Mirth increased permissiveness for deontological violations, whereas elevation had the opposite effect. Furthermore, affective valence had no apparent independent influence on these judgments. Our results suggest that mirth and elevation have distinct cognitive consequences whose properties reflect their respective social functions, not their shared positive valence.

Dual-route processing of complex words: New fMRI evidence from derivational suffixation

Many behavioral models of the comprehension of suffixed words assume a dual-route mechanism in which these words are accessed sometimes from the mental lexicon as whole units and sometimes in terms of their component morphemes (such as happi+=ness). In related neuropsychological work, Ullman et al. (1997) proposed a dual-route model for past tense processing, in which the lexicon (used for access to irregularly inflected forms) corresponds to declarative memory and a medial temporal/ parietal circuit, and the rule system (used for computation of regularly inflected forms) corresponds to procedural memory and a frontal (including Broca’s area)/basal ganglia circuit. We used functional MRI and a memory encoding task to test this model for derivationally suffixed words, comparing those words that show evidence of decompositional processing in behavioral studies (-ness, -less, and -able words) with derived words that do not show decomposition effects (-ity and -ation words). By examining Broca’s area and the basal ganglia as regions of interest, we found that “decomposable” derived and inflected words showed increases in activity relative to nondecomposable suffixed words. Results support a dual-route model of lexical access of complex words that is consistent with the Ullman et al. proposal.

Falsifying Serial and Parallel Parsing Models: Empirical Conundrums and An Overlooked Paradigm

When the human parser encounters a local structural ambiguity, are multiple structures pursued (parallel or breadth-first parsing), or just a single preferred structure (serial or depth-first parsing)? This note discusses four important classes of serial and parallel models: simple limited parallel, ranked limited parallel, deterministic serial with reanalysis, and probabilistic serial with reanalysis. It is argued that existing evidence is compatible only with probabilistic serial-reanalysis models, or ranked parallel models augmented with a reanalysis component. A new class of linguistic structures is introduced on which the behavior of serial and parallel parsers diverge the most radically: multiple local ambiguities are stacked to increase the number of viable alternatives in the ambiguous region from two to eight structures. This paradigm may provide the strongest test yet for parallel models.