A secondary-task analysis of a word familiarity effect

In three experiments we examined aspects of the word inferiority effect and word frequency disadvantage for letter detection. In Experiment 1 we tested a prediction derived from a hypothesis based solely on attentional factors. Adult subjects performed one of two secondary detection tasks while reading for comprehension. The inferiority effects were obtained only when the secondary task was letter detection, not when nonletter targets were used in the secondary task. This finding is inconsistent with the attentional hypothesis, but is consistent with the unitization hypothesis of Healy and Drewnowski (1983). In Experiments 2 and 3 we found that manipulation of the need to read for comprehension had little influence on the letter-detection inferiority effects, but a strong influence on the effects involving the detection of nonletter targets. These results are discussed in terms of their implications concerning processing system flexibility.     

Distributed memory and the representation of general and specific information

We describe a distributed model of information processing and memory and apply it to the representation of general and specific information. The model consists of a large number of simple processing elements which send excitatory and inhibitory signals to each other via modifiable connections. Information processing is thought of as the process whereby patterns of activation are formed over the units in the model through their excitatory and inhibitory interactions. The memory trace of a processing event is the change or increment to the strengths of the interconnections that results from the processing event. The traces of separate events are superimposed on each other in the values of the connection strengths that result from the entire set of traces stored in the memory. The model is applied to a number of findings related to the question of whether we store abstract representations or an enumeration of specific experiences in memory. The model simulates the results of a number of important experiments which have been taken as evidence for the enumeration of specific experiences. At the same time, it shows how the functional equivalent of abstract representations--prototypes, logogens, and even rules--can emerge from the superposition of traces of specific experiences, when the conditions are right for this to happen. In essence, the model captures the structure present in a set of input patterns; thus, it behaves as though it had learned prototypes or rules, to the extent that the structure of the environment it has learned about can be captured by describing it in terms of these abstractions.     

A computational analysis of mental image generation: evidence from functional dissociations in split-brain patients

Recent efforts to build computer simulation models of mental imagery have suggested that imagery is not a unitary phenomenon. Rather, such efforts have led to a modular analysis of the image-generation process, with separate modules that can activate visual memories, inspect parts of imaged patterns, and arrange separate parts into a composite image. This idea was supported by the finding of functional dissociations between the kinds of imagery tasks that could be performed in the left and right cerebral hemispheres of two patients who had previously undergone surgical transection of their corpus callosa. The left hemisphere in both subjects could inspect imaged patterns and could generate single and multipart images. In contrast, although the right hemisphere could inspect imaged patterns and could generate images of overall shape, it had difficulty in generating multipart images. The results suggest a deficit in the module that arranges parts into a composite. The observed pattern of deficits and abilities implied that this module is not used in language, visual perception, or drawing. Furthermore, the results suggest that the basis for this deficit is not a difficulty in simply remembering visual details or engaging in sequential processing.     

Potentiation and overshadowing in preweanling and adult rats

Four experiments compared the aversion acquired by 18-day-old and 60-day-old rats to a flavor that was either tasted alone or in combination, simultaneously or successively, with another flavor when paired with illness. The purpose was to study temporal variables and theoretical issues pertinent to potentiation and overshadowing while investigating ontogenetic differences in these phenomena. When either the preweanlings or the adults were presented a simultaneous compound flavor (sucrose/coffee) followed by lithium chloride-induced illness, greater sucrose aversions were found than for animals conditioned on sucrose alone--that is, potentiation. Preweanlings demonstrated greater potentiation than did adults, whether the conditioned stimulus-unconditioned stimulus (CS-US) delay was 0 or 1 hr. This potentiation was eliminated by nonreinforced presentations of the alternative CS element. Potentiation was not seen when the two flavors were presented successively as the CS; instead, overshadowing occurred. Tests of configuring by extinction procedures indicated a tendency for these animals to form a configured representation of the simultaneous compound solution. This disposition for configuring tended to be more pronounced for preweanlings than for adults. Ontogenetic differences in response to configuration, CS saliency, and generalization decrement seem consistent with at least one model of potentiation and the ontogenetic differences in potentiation seen in the present experiments.     

Discrimination of letters and random dot patterns by pigeons and humans

In a three-choice discrimination task, pigeons learned to distinguish each letter of the alphabet from all the other letters and each of 16 random dot patterns from all the others. Discrimination errors were used to generate a matrix of interletter and interpattern similarities. Human estimates of letter similarity were obtained from the literature, and human subjects rated the similarity of the dot patterns. Pigeon and human performances were described and compared through correlation, multidimensional scaling, and cluster analysis. Fits of the data by simple-feature and template models were computed and compared. The correlation between pigeon and human similarity matrices was .68 for letters and .72 for dot patterns. The other analyses revealed broadly similar patterns of results from the two species but suggested also that, relative to human data, the best fits to the pigeon data required fewer dimensions, fewer features, and fuzzier templates. There was some indication that pigeon discriminations depended on relatively simple features, and several of these were tentatively identified. The different methods employed might have influenced these apparent differences between pigeons and humans, but, overall, the results suggest considerable cross-task and cross species generality in the processing of these simple forms.     

Effect of classical conditioning on an internal clock

Six experiments with rats used a psychophysical choice procedure to study the internal clock used to discriminate duration. They investigated if the clock is sensitive to the signal value (associative strength) of a stimulus. The experiments involved two types of trials. On choice trials, a stimulus lasted a short (e.g., 3 s) or long (e.g., 12 s) duration; then the rats chose between two levers. The rewarded choice depended on the duration of the stimulus. On conditioning trials, the stimulus used on choice trials was presented, but it ended without food (extinction trials) or with food (pairing trials) regardless of what the rat did. The main stimulus minus accuracy with the long stimulus. Experiment 1 showed that extinction trials increased short bias relative to training without conditioning trials or to training with pairing trials. The rest of the experiments tested explanations of these results. The same results were found when extinction trials were the same duration as the short stimulus (Experiment 2), when extinction trials were a random duration (Experiment 5), and when the signal value of the conditioned stimulus was changed in another way (Experiment 6). The effect of conditioning trials was modality specific (Experiments 3 and 4). Of the explanations considered, the best one--the only one not contradicted at least once--is that changing the signal value of a stimulus changes how the clock times the stimulus. Reducing signal value reduces the measured duration.     

Treatment of chronic global aphasia with a nonverbal communication system

Four chronic global aphasics were treated with Blissymbols (C. K. Bliss, 1965, Semantography-Blissymbolics, Sydney: Semantography Pub.). As soon as possible the therapeutic communication was based solely on the use of the symbols. Three patients seemed to benefit from therapy. In one case therapy had to be discontinued because of massive perseveration. In one patient expression of needs relied solely on the use of the symbols. In another, expressive speech could be restored to such an extent that communication by the use of symbols was discontinued.     

The word-superiority effect under conditions that approximate reading

Observers detected a briefly flashed target letter embedded in word, pronounceable nonword, and unpronounceable nonword contexts. The word context facilitated perception under both holistic and analytical processing strategies; the facilitative effect was enhanced when processing was analytical.     

Stuttering and the valsalva mechanism: A hypothesis in need of investigation

This note presents the hypothesis than the excessively forceful closure of the mouth of larynx associated with certain types of stuttering may involve a neurological confusion between speech and the human body's Valsalva mechanism, which is designed to increase pulmonary pressure by forceful closure of the upper airway to assist in many types of physical effort. It is suggested that such behavior may result from excessive neuromotor tuning of the Valsalva mechanism prior to speech, especially in situations where the stutterer anticipates the need to “try hard” to speak properly. Such tuning may both interfere with phonation and render the Valsalva mechanism overexcitable to triggering stimuli, such as the increase in subglottal pressure that accompanies the start of articulation.     

Early adolescent egocentrism: a review of six articles

This paper reviews six articles which appear to be representative of the past fifteen years during which researchers have focused on early adolescent egocentrism. Each article is described in chronological order and compared to research findings suggested by the other articles. Although the researchers have suggested some interesting associations, there is a lack of consistency among their findings. The author indicates methodological problems and questions for further research which arise from the reviewed articles.