Variability in prescription opioid intake and reinforcement amongst 129 substrains.

Opioid abuse in the United States has reached epidemic proportions, with treatment admissions and deaths associated with prescription opioid abuse quadrupling over the past 10 years. Although genetics are theorized to contribute substantially to inter-individual variability in the development, severity and treatment outcomes of opioid abuse/addiction, little direct preclinical study has focused on the behavioral genetics of prescription opioid reinforcement and drug-taking. Herein, we employed different 129 substrains of mice currently available from The Jackson Laboratory (129S1/SvlmJ, 129X1/SvJ, 129S4/SvJaeJ and 129P3/J) as a model system of genetic variation and assayed mice for oral opioid intake and reinforcement, as well as behavioral and somatic signs of dependence. All substrains exhibited a dose-dependent increase in oral oxycodone and heroin preference and intake under limited-access procedures and all, but 129S1/SvlmJ mice, exhibited oxycodone reinforcement. Relative to the other substrains, 129P3/J mice exhibited higher heroin and oxycodone intake. While 129X1/SvJ exhibited the highest anxiety-like behavior during natural opioid withdrawal, somatic and behavior signs of precipitated withdrawal were most robust in 129P3/J mice. These results demonstrate the feasibility and relative sensitivity of our oral opioid self-administration procedures for detecting substrain differences in drug reinforcement/intake among 129 mice, of relevance to the identification of genetic variants contributing to high vs. low oxycodone reinforcement and intake.

Learning of nondomain facts in high- and low-knowledge domains.

Research on expertise has repeatedly documented that experts learn new information better than do novices, but only when the information is relevant to the expert's domain. It was found in Experiment 1 that participants showed superior learning and recall of a large quantity of new, non-domain-relevant facts about concepts within their domain of high knowledge than about concepts for which they had low domain knowledge. Experiment 2 investigated whether the participants' superior recall of new facts related to concepts within their domain of high knowledge was due to the number of prior facts associated with the concept or to the prior frequency of repetition of those concepts. It was found that participants' recall of new facts was better for concepts with 5 prior associated facts than for concepts with a single prior association but that the number of previous repetitions of each concept did not affect the level of recall for the new facts.

Retention and transfer of morse code reception skill by novices: part-whole training.

The training of composite skills requiring differential responding to a large set of stimuli raises issues about how to break down the whole task into parts and which parts should be trained first. Components of Morse code reception skill were identified, separated, and used to test whether initial training on a difficult part was more effective than initial training on an easy part. Initial training on a difficult subset of stimuli and on a difficult subtask both yielded disadvantages rather than the advantage implied by recent findings with different tasks. Incremental training should begin with the part yielding the most effective strategic skills, which appear to depend on characteristics of the task. In both present experiments, easy initial training led to adoption of an effective unitization strategy for representing codes. The hypothesis that procedural reinstatement at delayed testing leads to better retention was supported and extended.

Processes underlying long-term repetition priming in digit data entry.

Two experiments examined long-term repetition priming in data entry. In each experiment, participants entered 4-digit numbers displayed as either words or numerals, and responded with digits (Experiment 1), or either digits or initial letters (Experiment 2). At test 1 week later, they entered old and new numbers, with the format changed for half of the old stimuli. Implicit memory was evidenced at test by faster entry of the old than the new numbers, regardless of whether the numbers were in the same or different format, suggesting that the abstract numerical meaning, not the surface form, contributes to repetition priming. Numbers presented as words in training had an advantage over numbers presented as numerals, regardless of response format, implying that type of processing also contributes to the effect and ruling out an explanation based on time spent processing numbers in word format.

Sentence interference in the Stroop task.

In two experiments on Stroop interference, we examined whether sentences can be processed without the intention of the reader. Participants named the ink colors in which words in sentences were printed, and the ink colors in which the same words, randomly arranged, were printed. In Experiment 1, sentences yielded longer response times (RTs) and more errors than did nonsentences, but only when they included words that were highly relevant to the color-naming task (i.e., color and color-related words). In Experiment 2, sentences yielded more errors than did nonsentences, and sentences in which the color words matched the set of ink colors yielded longer RTs than did nonsentences. The results indicate that sentence processing can be obligatory when the component words are highly relevant to the task.

The role of item distinctiveness in short-term recall of order information.

In two experiments, we examined short-term recall of order information using a partial-report distractor task. We manipulated the characteristics of a single letter in one of two four-letter segments. Participants knew in advance the identity of the letters in each segment. We made a single letter distinctive at presentation either by printing it in red or by replacing it with a red dash. Presenting the letter in red did not affect overall recall of the positions of the letters in the segment but did facilitate specific recall of the position of the distinct letter. Replacing the letter with a red dash inhibited overall recall as well as specific recall of the distinct letter. Participants were also less likely to respond in the regular output order when there was a dash replacing a letter in the segment. These effects of distinctiveness are explained in terms of output order processes in recent versions of the perturbation model.

The time-course of the generation effect.

The generation effect, in which items generated by following some rule are remembered better than stimuli that are simply read, has been studied intensely over the past two decades. To date, however, researchers have largely ignored the temporal aspects of this effect. In the present research, we used a variable onset time for the presentation of the to-be-remembered material, thus providing the ability to determine at what point during processing the generation effect originates. The results indicate that some benefit from generation attempts occurs even when subjects have only a few hundred milliseconds in which to process the stimulus, but that more of the benefit occurs later. This finding suggests that the generation effect results from continuous or multiple discrete stages of information accrual or strengthening of memory traces over time, rather than from a single discrete increment upon final generation.

Verbal learning and memory: does the modal model still work?

This chapter focuses on recent research concerning verbal learning and memory. A prominent guiding framework for research on this topic over the past three decades has been the modal model of memory, which postulates distinct sensory, primary, and secondary memory stores. Although this model continues to be popular, it has fostered much debate concerning its validity and specifically the need for its three separate memory stores. The chapter reviews research supporting and research contradicting the modal model, as well as alternative modern frameworks. Extensions of the modal model are discussed, including the search of associative memory model, the perturbation model, precategorical acoustic store, and permastore. Alternative approaches are discussed including working memory, conceptual short-term memory, long-term working memory, short-term activation and attention, processing streams, the feature model, distinctiveness, and procedural reinstatement.

Searching for target letters in memory: Individual preferences and instructions for text representation.

Participants searched for target letters in a short passage held in memory. In Experiment 1, participants were divided into two groups on the basis of a retrospective report concerning the type of representation used to store the passage in memory, and in Experiment 2, participants were instructed concerning the form of memory representation to use. Only participants using a visual representation missed more targets in the wordthe than in other words. Participants instructed to form a visual representation also made fewer content-word or phrase substitutions when learning the passage than did participants instructed to form an auditory representation. These findings show that choice of memory representation is flexible and that the representation used influences what can be retrieved from memory.

Letter detection: A window to unitization and other cognitive processes in reading text.

Experiments are reviewed that use the letter-detection task, in which subjects read text and circle target letters. Evidence is provided that the letter-detection task reveals the processing units used in reading text and is influenced as well by visual, phonetic, and a combination of semantic and syntactic factors. Specifically, it is shown that circling a target letter in a word depends on the familiarity of the word's visual configuration, the location of the word in the reader's visual field, the phonetic representation of the letter in the word, and a combination of the word's meaning and its grammatical function.

Detecting phonemes and letters in text: interactions between different types and levels of processes.

In six experiments, subjects detected phonemes or letters in text presented auditorily or visually. Experiments 1 and 2 provided support for the hypothesis that a mismatch between the phoneme and letter representations of a target leads to detection errors. In addition, visual word unitization processes were implicated. Experiments 3 and 4 provided support for the hypothesis that the Gestalt goodness of pattern affected detection errors when subjects searched for letters. Experiments 5 and 6 demonstrated that the effects of unitization on the detection of letters in common words were decreased by altering the familiar configuration of the test words. The combined results of all six experiments lead to the conclusion that both visual and phonetic processes influence letter detection, that these processes communicate through a type of cross-checking, and that there are at least two levels of visual (and perhaps of phonetic) processing involved in the letter detection task.

Is there really very rapid forgetting from primary memory? The role of expectancy and item importance in short-term recall.

In two experiments, subjects recalled one of two letter segments following a digit-filled retention interval. In Experiment 1, recall expectancy was manipulated by using precues that correctly informed or misinformed subjects concerning which letter segment would be tested for recall. In Experiment 2, item importance was varied by precuing one segment as important but requiring that the uncued segment be recalled first. Recall performance was very low under conditions of low expectancy and low segment importance, but the slopes of the retention functions did not demonstrate more rapid forgetting than under standard conditions. The previous observations of very rapid forgetting from primary memory may be a function of an elevated initial recall level in the earlier studies. Our retention functions were compared with predictions of the Estes perturbation model. The findings suggested that when secondary memory processes were reduced, forgetting order information from primary memory occurred at the same rate as that estimated on the basis of previous studies using the standard distractor task.

Checklist procedures and the cost of automaticity.

Automaticity is usually discussed in terms of its benefits. Automaticity has, however, a cost that manifests itself in procedures that are highly routinized but require close attention, such as verbal checklist procedures. In such procedures, errors occur because the routine leads to automaticity. In three paper-and-pen experiments, we tested this manifestation and investigated ways to decrease automaticity in verbal checklist procedures. In the experiments, subjects proofread sets of multiplication problems to detect erroneous operations, simulating the checklist procedure. In Experiments 1 and 2, two conditions were compared: a fixed-order condition (in which each set contained operations in the same order) and a varied-order condition (in which the operations were in a different order in each set). In Experiment 1, proofreading times were measured to establish the role of fixed sequential order as a consistent environment promoting the emergence of automaticity. In Experiment 2, we introduced errors into the material, and in Experiment 3 we introduced "alerting" conditions to interfere with the development of automaticity. The results indicated that the subjects in the varied-order and alert conditions detected significantly more errors than did those in the fixed-order condition. The implications of the findings for current theories of automaticity are discussed as well as those for the design of checklist procedures.

A developmental evaluation of the role of word shape in word recognition.

Fourth- and seventh-grade children and college-age adults proofread passages typed either in lowercase or in all capital letters. Words were misspelled by deleting one of four letters, s, c, k, or p, that have similar features in lowercase and uppercase. Proofreading errors decreased with age and increasing reading ability, but all of the subjects were sensitive to changes in word shape--they missed more words with deletions of s or c than k or p in the lowercase passage but not in the all-capitals passage. These findings indicate that word shape is an important variable in recognizing familiar words, even for young readers.

Output and retrieval interference in the missing-number task.

Three experiments are reported that represent a reexamination of the missing-number method (Buschke, 1963b) of estimating short-term memory span. The missing-number task involved presenting a random sequence of all but one of the numbers of a known reference set and asking subjects to identify the missing number. Experiment 1 introduced a modified missing-number task that included two missing items and two choices made by the subject. With a large decline in performance for the second choice relative to the first, it is possible that only the second choice was subject to output or retrieval interference. An alternative explanation is that subjects output the number with the weakest memory representation as their first response. By postcuing subjects to report their two choices in a forward or backward sequence, Experiment 2 provided evidence against the importance of output interference and support either for the importance of retrieval interference or for the "weakest-first" hypothesis. However, with a paradigm that replaced only correctly identified missing numbers, a prediction that subjects would select the number with the weakest memory representation as their first response was not confirmed in Experiment 3. Instead, retrieval interference was implicated to explain the first-choice superiority found in Experiments 1 and 3. The results were interpreted in terms of the TODAM model of Murdock (1982, 1987, in press).

Syllable-internal structure and the sonority hierarchy: differential evidence from lexical decision, naming, and reading.

Treiman (1983) and others have argued that spoken syllables are best characterized not as linear strings of phonemes, but as hierarchically organized units consisting of an onset (initial consonant or consonant cluster) and a rime (the vowel and any following consonants) and that the rime is further divided into a peak or nucleus (the vowel) and a coda (the final consonants). It has also been argued that the sonority (or vowel-likeness) of the consonant closest to the peak, which is a function of its phonetic class, may have an effect on the strength of boundaries determined by the hierarchical division of the syllable (e.g., Treiman, 1984). We examined the evidence for syllable-internal structure and for sonority in two experiments that employed visually presented stimuli and lexical decision, naming, and reading tasks. Our results provide support for the breakdown of the rime into a peak and a coda and for an effect of the sonority of the postvocalic consonant on that break. This pattern occurred only in our lexical decision tasks, so the effect is assumed to be postlexical. We did not find an effect of the onset-rime boundary, perhaps because of an unanticipated effect of word frequency. Our results are discussed in terms of phonological coding in short-term memory.

Same-different judgments of multiletter strings: insensitivity to positional bias and spacing.

Several recent studies of multiletter matching have included pairs of strings that have the same letters in different positions (rearranged pairs). The task can be defined such that these rearranged pairs are correctly classified as different (i.e., subjects respond "same" only if the strings have the same letters in the same positions--the order task) or as same (i.e., subjects respond "same" if the strings have the same letters regardless of their positions--the item task). The order task produces left-to-right serial-position effects, whereas the item task produces U-shaped serial-position effects. Because these differences suggest that subjects may be able to exert strategic control over the comparison process, two sets of experiments were designed to test whether or not subjects can change the relative weightings devoted to the respective serial positions. In Experiments 1 and 2, the probability that a mismatch occurred in the different positions was manipulated. In Experiments 3 and 4, the physical spacing between letters, as well as whether or not the spaces were filled with neutral noise characters, was varied. None of the manipulations had much influence on the serial-position effects. Thus, the distinct serial-position effects for the order and item tasks apparently are mandatory and not due to any voluntary comparison strategy.

Long-term repetition effects for motoric and perceptual procedures.

Two experiments examined the relationship between implicit and explicit measures of memory for information encoded in a motoric task, called data entry. In both experiments, subjects entered lists of digit sequences with a computer keypad. They were retested on the same task after a delay of up to 1 month. At retention, implicit memory for the digit lists was evidenced by faster entry of old relative to new lists in both experiments. In Experiment 1, subjects were able to discriminate old from new lists. Recognition memory of old lists was better after than before entering the lists. In Experiment 2, perceptual and motoric contributions to the old/new difference in typing speed were isolated by means of a transfer paradigm. The results showed that the entry-speed advantage for the old lists was due to the separate reinstatement at the retention test of both perceptual and motoric procedures encoded earlier. Implicit and explicit measures of memory were found to be dependent rather than independent. The findings from this study are interpreted within a framework of memory based on procedural reinstatement.

Acquisition and retention of a letter-detection skill.

In two experiments, we examined the acquisition and retention of a letter-detection skill with a consistent-mapping procedure. In Experiment 1, subjects were trained from 0 to 4 sessions at detecting the letter H in displays containing random letters, and retesting occurred after a 1-month delay. Performance improved and in some cases became more automatic, and the performance level was maintained over the retention interval. When tested with a prose passage, the high error rate on the word THE was eliminated after training and after the retention interval, regardless of the amount of training. In Experiment 2, two subjects were given 12 sessions of training followed by a retention test 6 months later. For 1 subject there was also a retention test 15 months after acquisition. Performance improved dramatically with training, and substantial but not complete automaticity was achieved. Performance on the retention tests was close to the final acquisition level. The surprising lack of forgetting in this study was contrasted with the substantial forgetting typically found in studies of verbal learning.

Identification of letters in the predesignated target paradigm: a word superiority effect for the common word the.

The size of the perceptual unit used in reading was addressed using the predesignated target paradigm. Sixteen subjects viewed the following stimuli in random order: the words tee, the, tie, and toe; the nonwords eet, eht, eit, and eot; and the letters e, h, i, and o. Subjects fixated on the location of the center letter and identified the letter as e, h, i, or o, alternatives which were known to them at the onset. A word superiority effect was obtained for the common word the but not for the less common words tee, tie, and toe. The word superiority effect was attributable to bias rather than discriminability: Subjects exhibited a bias to perceive the words in this experiment as the (i.e., there was a bias to perceive h in the t e stimulus presentations). These results suggest that the common word the is processed in reading units that are larger than the letter, and that the system is biased to perceive common rather than uncommon words in data-limited conditions.