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R Ratcliff

Publications and source records attributed to R Ratcliff.

17 recordsLinked to original sources
PubMed1992

Disruption of the cystic fibrosis transmembrane conductance regulator gene in embryonic stem cells by gene targeting.

We have successfully disrupted the cftr (cystic fibrosis transmembrane conductance regulator) gene at its endogenous locus in embryonic stem cells by gene targeting. We are using a double replacement strategy to introduce subtle mutations into exon 10. We report here the first step of creating a null mutation by insertion of a functional hprt (hypoxanthine phosphoribosyl transferase) mini-gene into exon 10 of the cftr gene. Targeted embryonic stem cell clones were identified by PCR screening and confirmed by Southern blot analysis. One of the cftr targeted clones has been injected into recipient blastocysts and shown to contribute to chimaeras. The targeted clones will now be used as the starting point for a second gene targeting step to remove the hprt gene in exon 10 with the concomitant introduction of the delta F508 mutation or other mutations.

Animals↗
PubMed1992

Pronoun resolution and discourse models.

Psychological investigations of pronoun resolution have implicitly assumed that the processes involved automatically provide a unique referent for every pronoun. We challenge this assumption and propose a new framework for studying pronoun resolution. Drawing on advances in discourse representation and global memory modeling, this framework suggests that automatic processes may not always identify a unique referent for a pronoun. In 9 experiments, we demonstrate that, unlike noun anaphors, pronouns sometimes do not produce relative facilitation of their referents in comparison with nonreferents. We argue that research on pronoun resolution must consider the discourse contexts in which pronouns are likely to occur.

Attention↗
PubMed1992

Spreading activation versus compound cue accounts of priming: mediated priming revisited.

Spreading activation theories and compound cue theories have both been proposed as accounts of priming phenomena. According to spreading activation theories, the amount of activation that spreads between a prime and a target should be a function of the number of mediating links between the prime and target in a semantic network and the strengths of those links. The amount of activation should determine the amount of facilitation given by a prime to a target in lexical decision. To predict the amount of facilitation, it is necessary to measure the associative links between prime and target in memory. Free-association production probability has been the variable chosen in previous research for this measurement. However, in 3 experiments, the authors show priming effects that free-association production probabilities cannot easily predict. Instead, they argue that amount of priming depends on the familiarity of the prime and target as a compound, where the compound is formed by the simultaneous presence of the prime and target in short-term memory as a test item.

Adult↗
PubMed1992

Inference during reading.

Most current theories of text processing assume a constructionist view of inference processing. In this article, an alternative view is proposed, labeled the minimalist hypothesis. According to this hypothesis, the only inferences that are encoded automatically during reading are those that are based on easily available information, either from explicit statements in the text or from general knowledge, and those that are required to make statements in the text locally coherent. The minimalist hypothesis is shown to be supported by previous research and by the results of several new experiments. It is also argued that automatically encoded minimalist inferences provide the basic representation of textual information from which more goal-directed, purposeful inferences are constructed.

Attention↗
PubMed1992

Testing global memory models using ROC curves.

Global memory models are evaluated by using data from recognition memory experiments. For recognition, each of the models gives a value of familiarity as the output from matching a test item against memory. The experiments provide ROC (receiver operating characteristic) curves that give information about the standard deviations of familiarity values for old and new test items in the models. The experimental results are consistent with normal distributions of familiarity (a prediction of the models). However, the results also show that the new-item familiarity standard deviation is about 0.8 that of the old-item familiarity standard deviation and independent of the strength of the old items (under the assumption of normality). The models are inconsistent with these results because they predict either nearly equal old and new standard deviations or increasing values of old standard deviation with strength. Thus, the data provide the basis for revision of current models or development of new models.

Adult↗
PubMed1990

List-strength effect: II. Theoretical mechanisms.

Ratcliff, Clark, and Shiffrin (1990) examined the list-strength effect: the effect of strengthening (or weakening) some list items upon memory for other list items. The list-strength effect was missing or negative in recognition, missing or positive in cued recall, and large and positive in free recall. We show that a large number of current models fail to predict these findings. A variant of the SAM model of Gillund and Shiffrin (1984), involving a differentiation hypothesis, can handle the data. A variant of MINERVA 2 (Hintzman, 1986, 1988) comes close but has some problems. Successful variants of a variety of composite and network models were not found (e.g., Ackley, Hinton, & Sejnowski, 1985; Anderson, 1972, 1973; Metcalfe Eich, 1982; Murdock, 1982; Pike, 1984). The results suggest constraints on the future development of such models.

Cues↗
PubMed1990

Connectionist models of recognition memory: constraints imposed by learning and forgetting functions.

Multilayer connectionist models of memory based on the encoder model using the backpropagation learning rule are evaluated. The models are applied to standard recognition memory procedures in which items are studied sequentially and then tested for retention. Sequential learning in these models leads to 2 major problems. First, well-learned information is forgotten rapidly as new information is learned. Second, discrimination between studied items and new items either decreases or is nonmonotonic as a function of learning. To address these problems, manipulations of the network within the multilayer model and several variants of the multilayer model were examined, including a model with prelearned memory and a context model, but none solved the problems. The problems discussed provide limitations on connectionist models applied to human memory and in tasks where information to be learned is not all available during learning.

Attention↗
PubMed1990

List-strength effect: I. Data and discussion.

Extra items added to a list cause memory for the other items to decrease (the list-length effect). In one of the present studies we show that strengthening (or weakening) some items on a list harms (helps) free recall of the remaining list items. This is termed the list-strength effect. However, in seven recognition studies the list-strength effect was either absent or negative. This held whether strengthening was accomplished by extra study time or extra repetitions. The seven studies used various means to control rehearsal strategies, thereby providing evidence against the possibility that the findings were due to redistribution of rehearsal or effort from stronger to weaker items within a list. Current models appear unable to predict these results. We suggest that different retrieval operations underlie recall and recognition, as in the SAM model of Gillund and Shiffrin (1984), which can be made to fit the results with certain relatively minor modifications.

Cues↗
PubMed1989

Semantic associations and elaborative inference.

In this article, a theoretical framework is proposed for the inference processes that occur during reading. According to the framework, inferences can vary in the degree to which they are encoded. This notion is supported by three experiments in this article that show that degree of encoding can depend on the amount of semantic-associative information available to support the inference processes. In the experiments, test words that express possible inferences from texts are presented for recognition. When testing is delayed, with other texts and test items intervening between a text and its test word, performance depends on the amount of semantic-associative information in the text. If the inferences represented by the test words are not supported by semantic associates in the text, they appear to be only minimally encoded (replicating McKoon & Ratcliff, 1986), but if they are supported by semantic associates, they are strongly encoded. With immediate testing, only 250 ms after the text, performance is shown to depend on semantic-associative information, not on textual information. This suggests that it is the fast availability of semantic information that allows it to support inference processes.

Adult↗
PubMed1989

A bias interpretation of facilitation in perceptual identification.

In a typical perceptual identification task, a word is presented for a few milliseconds and masked; then subjects are asked to report the word. It has been found that an earlier presentation of the test word will improve identification of the test word by as much as 30%. In addition, this facilitation has been shown to be preserved under amnesia. In this article we examine a fundamental question: Is the facilitation the result of bias toward the earlier presented item, an improvement in perceptual sensitivity, or both? The experiments presented here use a forced choice procedure to show that prior presentation of an item biases the subject to choose that item but does not improve discriminability. This result is obtained when the distractor items are visually similar to the target items. When distractors are dissimilar, earlier presentation affects neither bias nor discriminability. Two models of word identification are examined in light of the bias effects, and implications for understanding savings in amnesia are also examined.

Adult↗
PubMed1989

Time course of item and associative information: implications for global memory models.

The time course of availability of associative and item information was examined by using a response signal procedure. Associative information discriminates between a studied pair of words and a pair with words from two different studied pairs. Item information is sufficient to discriminate between a studied pair and a pair not studied. In two experiments, discriminations that require associative information are delayed relative to those based on item information. Two additional experiments discount alternative explanations in terms of the time to encode the test items or task strategies. Examination of the global memory models of Gillund and Shiffrin (1984), Hintzman (1988), and Murdock (1982) shows that the models treat item and associative information inseparably. Modifications to these models which can produce separate contributions for item and associative information do not predict any difference in their availability. Two possible mechanisms for the delayed availability of associative information are considered: the involvement of recall in recognition and the time required to form a compound cue.

Adult↗