The phonological similarity effect in immediate recall: positions of shared phonemes.

Earlier literature proposes two ways phonological similarity could harm immediate recall: (1) It could increase the degradation of the representations of items in memory, or (2) it could decrease the probability that a degraded representation is correctly reconstructed. A multinomial processing tree model for each hypothesis was used to analyze an immediate recall experiment. Both gave a good account of the data, but, of the two, results favor the hypothesis that the effect of phonological similarity is to impair reconstruction of degraded representations. A second issue is whether positions of repeated phonemes in phonologically similar items matter. We found that mere repetition of phonemes produced a phonological similarity effect. Repeated phonemes in the same positions appeared to produce a greater effect. A final finding is that when reading rate was preequated, phonological similarity affected memory span by changing the time taken to recall a list of span length.

Selective Influence and Response Time Cumulative Distribution Functions in Serial-Parallel Task Networks.

We analyze sets of mental processes, some of which are concurrent and some of which are sequential, under the assumption that the processes are partially ordered, that is, arranged in a directed acyclic network. Information about the process arrangement can be discovered by examining the effects on response time of selectively influencing process durations. Previous work has mainly focused on analyses of mean response times. Here we consider analyses based on cumulative distribution functions, for one of the major classes of directed acyclic networks, serial-parallel networks. When two processes are selectively influenced, patterns in the cumulative distribution functions can be used to test whether the processes are sequential or concurrent and whether the task network has AND gates or OR gates. Cumulative distribution functions are potentially more informative than means, and some previous results for means are shown to follow from our results for cumulative distribution functions. Copyright 2000 Academic Press.

Response time distributions: some simple effects of factors selectively influencing mental processes.

When hypotheses about mental processing are tested with response times, inferences are often based on means, and occasionally on variance or skewness. Calculations on entire distributions of response times are more informative and can be conveniently carried out. Recently investigators have been updating procedures primarily based on means (such as additive factors tests) to procedures employing entire distribution functions. In one such advance, Nozawa and Townsend upgraded earlier tests of whether factors selectively influence serial or parallel processes, and whether parallel processes enter AND gates or OR gates. We discuss generalizations of the tests to complex arrangements of processes in networks. Results for a particularly difficult network, the Wheatstone bridge, are presented here. We use simulations to demonstrate the feasibility of the tests, and the possibility of mimicking.

Word-frequency effects on short-term memory tasks: evidence for a redintegration process in immediate serial recall.

Four experiments investigated the mechanisms responsible for the advantage enjoyed by high-frequency words in short-term memory tasks. Experiment 1 demonstrated effects of word frequency on memory span that were independent of differences in speech rate. Experiments 2 and 3 showed that word frequency has an increasing effect on serial recall across serial positions, but Experiment 4 showed that this effect was abolished for backward recall. A model that includes a redintegration process that operates to "clean up" decayed short-term memory traces is proposed, and the multinomial processing tree model described by R. Schweickert (1993) is used to provide a quantitative fit to data from Experiments 2, 3, and 4.

Scheduling processes in working memory: instructions control the order of memory search and mental arithmetic.

Humans must often use working memory to execute processes one at a time because of its limited capacity. Two experiments tested where limits in access to working memory occur. Subjects searched a short-term memory set for one stimulus digit and performed mental arithmetic with another stimulus digit. In one experiment, they were told to carry out the mental arithmetic before the memory search and to make the arithmetic response first. In the other, they were instructed to perform the tasks in the opposite order. The overt responses were executed in the prescribed order. Moreover, the covert working memory processes were executed in the prescribed order, as revealed by a critical path network analysis of reaction times. Results are explained in terms of a double-bottleneck model in which central processes and responses are constrained to be carried out for one task at a time.

Cross-task cross talk in memory and perception.

The application of the additive factors method depends on finding factors that selectively influence processing stages. When all the processes for a task are in series, a factor directly influencing a process might change its output and thereby have indirect influence on succeeding processes. We investigate whether such indirect influence is possible between processes associated with different tasks being performed together. In two dual-task memory scanning and arithmetic experiments with digits as the stimuli for both tasks, information relevant for only one of the tasks nonetheless affected performance of the other. When the same digit was relevant for the two tasks, cross-task facilitation and interference were observed in some cases. Displaying the same digit for both tasks led to relatively fast response times, paralleling the effect of flankers in the response competition paradigm. But repetition of digits in memory slowed responses. It is suggested that the need for control processes to keep task information segregated is responsible for the pattern of effects.

Effects of generation on immediate memory span and delayed unexpected free recall.

We investigated the effects of generating words from fragments on pronunciation time, on immediate memory span, and on delayed free recall. Subjects read long words and short words aloud or generated them from strings with missing letters. Word-length and generation condition had multiplicative effects on speaking rate, as expected if each affected a separate process regulating the rate. We replicated the standard finding that span is smaller for longer words. Generation improved delayed free recall, indicating that relatively brief presentation times are adequate to produce a generation effect. Although generation improved long-term memory for the words, memory span was shorter for the words that were generated. The harmful effect of generation on span appears to be due to its slowing of speaking rate.

Effects on response time of factors selectively influencing processes in acyclic task networks with OR gates.

The mental processes involved in performing some tasks can be represented as directed arcs in an acyclic network. A path directed from the head of one arc to the tail of another indicates that the process represented by the first arc must be executed prior to the process represented by the second arc. If there is no directed path from one arc to another, the corresponding processes can be executed concurrently. Information about the arrangement of processes in an acyclic network can be found from the effects on response times of factors selectively influencing the processes. The methodology was developed earlier for critical path networks, in which a process begins execution when all its immediate predecessors have finished. This paper considers shortest path networks, in which a process begins execution as soon as any immediate predecessor is finished. Results analogous to those for critical path networks are reported. New results are presented enabling investigators to distinguish sequential and concurrent processes in both critical path and shortest path networks. This information is sufficient to construct an acyclic network representing the processes. Further, by examining the effects of selectively influencing processes, one can determine whether a task network is a critical path network or a shortest path network.

A multinomial processing tree model for degradation and redintegration in immediate recall.

When items are presented for immediate recall, a verbal trace is formed and degrades quickly, becoming useless after about 2 sec. The span for items such as digits equals the number of items that can be pronounced in the available time. The length of the items affects span by affecting pronunciation rate. Other properties, such as phonological similarity and lexicality, can affect span without affecting pronunciation rate. These properties change the trace's useful lifetime by affecting redintegration. An analogy is drawn between trace reconstruction and repair of errors in speech. When a trace is degraded, one process attempts to form a phoneme string, and another process attempts to form a word. The two processes are autonomous and can be selectively influenced by lexicality and phonological similarity. The resulting processing tree models make simple predictions that depend on whether or not the influenced processes are sequential. The results are illustrated with data from experiments by Besner and Davelaar (1982).

Separable effects of factors on activation functions in discrete and continuous models: d' and evoked potentials.

This article derives tests for partial-output models of information processing. A process in a partial-output model sends output, while executing, to its successors. In a stage model a process sends output to its successors only when it stops. Both models can be analyzed by manipulating factors, each affecting a different process. In discrete serial models, such factors have additive effects on reaction time (Sternberg, 1969) and sometimes on log percent correct (Schweickert, 1985). In partial-output models, such factors produce a simple pattern, the rectangle condition, in performance curves. Conditions for a partial-output representation are based on decomposable structures (Krantz et al., 1971). Tests of discrete and partial-output models are simultaneously satisfied only if performance is a linear function of time. Evoked potentials (Coles et al., 1985) and d' (Dosher, 1981) illustrate results.

Short-term memory capacity: magic number or magic spell?

Previous experiments have found that memory span is greater for items that can be pronounced more quickly. For a variety of materials the span equals the number of items that can be pronounced in about 1.5 s, presumably the duration of the verbal trace. This suggests a model for immediate recall: The probability of correctly recalling a list equals the probability that the time to recite the list is less than the variable duration of the trace. Recall probability for lists of various lengths was determined for six materials. Later, subjects read the lists aloud. The standard normal deviates corresponding to probability of correct recall were linear in pronunciation time. Evidently, over subjects, a normal distribution is a reasonable approximation of the distribution of the trace duration. The mean and variance of the trace duration were estimated. The mean (1.88 s) agrees well with previous estimates, and the model accounts for 95% of the variance in immediate recall.

Latent network theory: scheduling of processes in sentence verification and the Stroop effect.

A method for analyzing reaction times (RTs) in tasks involving both sequential and concurrent processing is proposed. Tasks are analyzed with the method by selectively prolonging mental processes, as with the additive factor method. Falsifiable predictions about the changes in RT produced by prolonging processes are derived by drawing on the theory of scheduling. Under certain conditions, which frequently arise in practice, one can determine for a given pair of processes whether they are executed sequentially or concurrently. If one process precedes another, one can often determine which comes first. One can also construct intervals within which the process durations lie. Two experiments are analyzed using the method. One, by Holyoak, Dumais, and Moyer, is on a sentence-verification task involving associated and unassociated items. The other experiment is on the Stroop effect and supports the single-channel hypothesis that a subject makes only one decision at a time. The data suggest that in the color-naming task the decision about the word precedes the decision about the color, whereas in the word-naming task the order of the decisions is reversed.

Critical-path scheduling of mental processes in a dual task.

Scheduling theory is used to extend the additive factors method of analyzing reaction times to tasks involving concurrent processing. Data indicate that mental processes in a double-stimulation experiment by Becker are executed in a critical-path network. A relationship predicted for the timing of the responses of the task is shown to hold.