Linguistic and conceptual control of visual spatial attention

A theory of voluntary, top-down control of visual spatial attention is presented that explains how linguistic cues like "above," "below," "left," and "right" are used to direct attention from one object to another. The theory distinguishes between perceptual and conceptual representations of space and views attention as a set of mechanisms that establish correspondences between the representations. Spatial reference frames play an important part in this analysis. The theory interprets reference frames as mechanisms of attention, similar to spatial indices but with more computational power. The theory was tested in 11 experiments that assessed the importance of linguistic distinctions between classes of spatial relations (basic, deictic, and intrinsic) and examined the flexibility with which subjects manipulated spatial reference frames.

Aging and inhibition: beyond a unitary view of inhibitory processing in attention

The authors examined the question of whether a decrease in the efficiency of inhibitory processing with aging is a general phenomenon. Thirty elderly and 32 young adults performed a series of tasks from which the authors could extract measures of inhibitory function. The tasks and task components included response compatibility, negative priming, stopping, spatial precuing, Wisconsin Card Sorting Test (WCST), and the Cognitive Failures Questionnaire (CFQ). Only limited evidence for age-related differences in inhibitory function was obtained. Old adults had more difficulty than young adults in stopping an overt response and adopting new rules in a categorization task. However, elderly and young adults produced equivalent negative priming effects, response compatibility effects, spatial precuing effects, and self-reported cognitive failures. The findings are discussed in terms of the relationship between aging, inhibitory processes, and neuroanatomical and physiological function.

Spatial attention and the apprehension of spatial relations

Seven experiments examined the role of spatial attention in apprehending spatial relations above, below, left, and right. In Experiment 1, visual search was difficult when targets differed from distractors only in the spatial relation between their elements. Reaction time increased linearly with display size with a slope greater than 60 ms/item. In Experiment 2, search was easy (the slope was flat) when targets differed from distractors in the identity of their elements. In Experiments 3 and 4, target position was cued with a discrepant color, and performance was better when attention was pulled toward spatial-relation targets than away from them. Experiments 5-7 generalized the results over different displays and extended practice. The results suggest that apprehending spatial relations requires spatial attention.

The loss of repetition priming and automaticity over time as a function of degree of initial learning

Two experiments were performed to investigate the buildup of repetition priming in a lexical decision task with repeated presentations and its decline over the course of 2 months. Priming was found to accumulate as a power function of presentations and to decline as a power function of time. Accuracy measures indicated that the loss rate of priming was unaffected by the amount of initial priming. Response time measures indicated the same result when the experiments were analyzed separately; however, when the data were combined, increased initial priming was associated with greater losses in priming over time. The data were interpreted in terms of automaticity, and the power function decline in priming was taken as support for memory-based models of automaticity. Possible ways to incorporate forgetting into memory-based theories of automaticity are discussed.

Memory-based automaticity in the discrimination of visual numerosity

In the development of memory-based models of automaticity, it is crucial to specify the nature of the memory representation. Seven experiments with 94 students use a counting task to determine whether a feature (i.e., identity, color, or orientation) is explicitly represented in memory. It is assumed that the degree of transfer to a pattern differing on one feature is determined by that feature's importance in supporting skilled performance. Experiment 1 determined the practice necessary to obtain automaticity. In Experiments 2a, 3a, and 4a, which investigated the nature of the representation after extended practice, changing neither the identity nor color of elements had strong effects on transfer, but changing pattern orientation did impair memory retrieval, thus suggesting that for the counting task, pattern orientation is more important than element identity or color. Experiments 2b, 3b, and 4b replicated these results after limited practice.

Evaluating a computational model of perceptual grouping by proximity

A formal approach to the phenomenon of perceptual grouping by proximity was investigated. Grouping judgments of random dot patterns were made by the CODE algorithm (van Oeffelen & Vos, 1982) and several related algorithms, and these judgments were compared with subjects' grouping judgments for the same stimuli. Each algorithm predicted significantly more subject judgments than would be expected by chance. The more subjects agreed on how a given dot pattern should be grouped, the more successful was the algorithms' ability to match the judgments for that pattern. CODE predicted significantly fewer subject judgments than did some of the other algorithms, largely because of its overemphasis on the extent of interactivity among dots as they are being grouped.

Shapes of reaction-time distributions and shapes of learning curves: A test of the instance theory of automaticity

The instance theory assumes that automatic performance is based on single-step direct-access retrieval from memory of prior solutions to present problems. The theory predicts that the shape of the learning curve depends on the shape of the distribution of retrieval times. One can deduce from the fundamental assumptions of the theory that (1) the entire distribution of reaction times, not just the mean, will decrease as a power function of practice; (2) asymptotically, the retrieval-time distribution must be a Weibull distribution; and (3) the exponent of the Weibull, which is the parameter that determines its shape, must be the reciprocal of the exponent of the power function. These predictions were tested and mostly confirmed in 12 data sets from 2 experiments. The ability of the instance theory to predict the power law is contrasted with the ability of other theories to account for it.

The transition from algorithm to retrieval in memory-based theories of automaticity

Two memory-based theories of automaticity were compared. The mixture model and the race model both describe automatization as a transition from algorithmic processing to memory retrieval. The mixture model predicts that, with training, the variability of reaction time will initially increase, and later decrease in a concave downward manner, whereas the race model predicts the variability will decrease only in a concave upward manner. The mixture model predicts that using both algorithm and retrieval on a single trial will be slower than using the algorithm alone, whereas the race model predicts the reverse. The experiments used an alphabet arithmetic task, in which subjects verified equations of the form H + 3 = K and made subjective reports of their strategies on individual trials. Both the variability of reaction times and the pattern of reaction times associated with the strategy reports supported the race model.

In search of the point of no return: the control of response processes

Control processes underlying response inhibition were examined. Six Ss performed a visual choice reaction task and were occasionally presented with a tone that told them to withhold the response. Reaction time results were in agreement with a model that assumes a race between response activation and response inhibition processes. Event-related brain potentials, electromyogram, and continuous response measures showed that responses could be interrupted at any time. Evidence was obtained for two inhibitory mechanisms: inhibition of central activation processes and inhibition of transmission of motor commands from central to peripheral structures. Results have implications for the distinction between controlled and ballistic processes.

Is there a search in fixed-set memory search?

We discuss the hypothesis that structural factors in the fixed-set memory-search task may contribute to the standard linear set-size effect typically observed in this task. We constructed a lexical decision task that contained the same structural factors as the memory-search task. Two structural factors are discussed: (1) the priming of the probe by the memory set, and (2) the confounding of repetitions per item with set size. Our experiment demonstrated that these structural factors play a role in the set-size effect. The implications of these effects for the memory-search task and for models proposed to account for memory-search data are discussed.

Effects of methylphenidate on inhibitory control in hyperactive children

This study investigated the effects of methylphenidate (MPH) on inhibitory control in hyperactive children. A double-blind, placebo-control, within-subject (crossover) design was used in which 12 children, between 6 and 11 years of age, were each tested four times in each drug condition: 0.3 mg/kg and 1.0 mg/kg of methylphenidate, and placebo. Dependent measures included (a) the probability of inhibiting responses to a primary choice reaction time task given a stop signal, on the Stopping Task, and (b) response latency and errors on the Matching Familiar Figures Test (MFFT). MPH improved the efficiency of the central inhibitory mechanism by speeding the inhibitory process, thereby affording the children greater control over their actions and enabling them to increase the probability with which they inhibited responses given a stop signal. MPH increased response latency but did not reduce errors on the MFFT, and observation of the children's task performance highlighted the interpretive problems associated with this task. Performance on both tasks was better at a dosage of 1.0 mg/kg than at 0.3 mg/kg.

Dose-response effects of methylphenidate on academic performance and overt behavior in hyperactive children

In the present study, the effects of 0.3 mg/kg and 1.0 mg/kg of methylphenidate on the overt behavior and academic functioning of 12 children with an established diagnosis of attention deficit disorder with hyperactivity were evaluated. A double-blind, placebo-control, within-subject (crossover) design was used, in which each child was tested four times in each drug condition. Drug conditions were alternated on a bidaily basis and each child received two different drug conditions each day. The academic tasks were designed for evaluation of the relationship between task complexity and dose. Whereas overt behavior improved with increasing dose, academic functioning was improved with methylphenidate, but did not vary with either dose or task complexity. Also, investigated were potential carryover effects of a morning dose of methylphenidate on performance in the afternoon. Behavioral and academic improvements produced by a dose of 0.3 mg/kg in the morning were no longer evident in the afternoon, but a morning dose of 1.0 mg/kg produced behavioral improvements that were clinically and statistically discernible in the afternoon, although the academic improvements had dissipated.

On the autonomy of mental processes: a case study of arithmetic

We define a process as autonomous if it can begin without intention, and if it can run on to completion without intention. We develop empirical criteria for determining whether a process can begin without intention, for determining whether it begins in the same way without intention as it does with intention, and for determining whether it can run on to completion without intention once it begins. We apply these criteria to assess the autonomy of the processes underlying simple mental arithmetic--the addition and multiplication of single digits--and find evidence that simple arithmetic may be only partially autonomous: It can begin without intention, but does not begin in the same way without intention as with intention and does not run on to completion without intention. This conclusion suggests there may be a continuum of autonomy, ranging from completely autonomous to completely nonautonomous.

On the autonomy of mental processes: A case study of arithmetic

We define a process as autonomous if it can begin without intention, and if it can run on to completion without intention. We develop empirical criteria for determining whether a process can begin without intention, for determining whether it begins in the same way without intention as it does with intention, and for determining whether it can run on to completion without intention once it begins. We apply these criteria to assess the autonomy of the processes underlying simple mental arithmetic--the addition and multiplication of single digits--and find evidence that simple arithmetic may be only partially autonomous: It can begin without intention, but does not begin in the same way without intention as with intention and does not run on to completion without intention. This conclusion suggests there may be a continuum of autonomy, ranging from completely autonomous to completely nonautonomous.

On the ability to inhibit simple and choice reaction time responses: a model and a method

This article reports four experiments on the ability to inhibit responses in simple and choice reaction time (RT) tasks. Subjects responding to visually presented letters were occasionally presented with a stop signal (a tone) that told them not to respond on that trial. The major dependent variables were (a) the probability of inhibiting a response when the signal occurred, (b) mean and standard deviation (SD) of RT on no-signal trials, (c) mean RT on trials on which the signal occurred but subjects failed to inhibit, and (d) estimated RT to the stop signal. A model was proposed to estimated RT to the stop signal and to account for the relations among the variables. Its main assumption is that the RT process and the stopping process race, and response inhibition depends on which process finishes first. The model allows us to account for differences in response inhibition between tasks in terms of transformations of stop-signal delay that represent the relative finishing times of the RT process and the stopping process. The transformations specified by the model were successful in group data and in data from individual subjects, regardless of how delays were selected. The experiments also compared different methods of selecting stop-signal delays to equate the probability of inhibition in the two tasks.

Constraints on strategy construction in a speeded discrimination task

In three experiments, subjects reported the identity of a word (above or below) that appeared above or below a fixation point. On some trials, a cue presented 100, 200, 400, 600, 800, or 1,000 msec before the word indicated the relation between position and identity (i.e., whether the dimensions were compatible, e.g., above/above and below/below, or conflicted, e.g., above/below and below/above). On the other trials, the cue was withheld (Experiment 2) or it bore no information about the relation between dimensions (Experiment 1 and 3). In each experiment, the cue reduced reaction time below the level of no-cue or neutral-cue controls, indicating strategic use of the relation between dimensions. Experiments 1 and 2 manipulated the number of potential cues that could occur in a block. A stronger cuing effect was found when one cue could occur (Experiment 2) than when two cues could occur (Experiment 1). Experiment 3 manipulated practice; it revealed that with practice the cuing effect reached asymptote at shorter delays. The asymptote itself did not change. Experiment 4 showed that cue-delay effects were independent of warning interval (warning interval and cue delay confounded in Experiment 1, 2, and 3). The experiments demonstrate construction and utilization of strategies; they show that construction is sensitive to constraints imposed by the subject's goals and abilities and by the structure of the task environment.

Constraints on strategy construction in a speeded discrimination task

In three experiments, subjects reported the identity of a word (above or below) that appeared above or below a fixation point. On some trials, a cue presented 100, 200, 400, 600, 800, or 1,000 msec before the word indicated the relation between position and identity (i.e., whether the dimensions were compatible, e.g., above/above and below/below, or conflicted, e.g., above/below and below/above). On the other trials, the cue was withheld (Experiment 2) or it bore no information about the relation between dimensions (Experiment 1 and 3). In each experiment, the cue reduced reaction time below the level of no-cue or neutral-cue controls, indicating strategic use of the relation between dimensions. Experiments 1 and 2 manipulated the number of potential cues that could occur in a block. A stronger cuing effect was found when one cue could occur (Experiment 2) than when two cues could occur (Experiment 1). Experiment 3 manipulated practice; it revealed that with practice the cuing effect reached asymptote at shorter delays. The asymptote itself did not change. Experiment 4 showed that cue-delay effects were independent of warning interval (warning interval and cue delay confounded in Experiment 1, 2, and 3). The experiments demonstrate construction and utilization of strategies; they show that construction is sensitive to constraints imposed by the subject's goals and abilities and by the structure of the task environment.

On the relation between identifying and locating masked targets in visual search

Three experiments were designed to determine whether naming is contingent on locating in a visual search task. Subjects were required to identify a masked target whose location was known (I|L) or unknown (I) and to locate a masked target whose identity was known (L|I) or unknown (L). The location-contingent hypothesis predicts a relationship among the tasks such that P(L) P(I|L) = P(I), since P(I) and P(L) P(I|L) both estimate the joint probability of identifying and locating the target (i.e. P(IλL)). This relationship held in Experiment I where targets were presented alone, and in Experiment II where targets were presented with dots as noise elements, but not in Experiment III where Xs were noise elements. The results are discussed in terms of the generality of the location-contingent hypothesis.