Dynamics of saccade target selection: race model analysis of double step and search step saccade production in human and macaque.

We investigated how saccade target selection by humans and macaque monkeys reacts to unexpected changes of the image. This was explored using double step and search step tasks in which a target, presented alone or as a singleton in a visual search array, steps to a different location on infrequent, random trials. We report that human and macaque monkey performance are qualitatively indistinguishable. Performance is stochastic with the probability of producing a compensated saccade to the final target location decreasing with the delay of the step. Compensated saccades to the final target location are produced with latencies relative to the step that are comparable to or less than the average latency of saccades on trials with no target step. Noncompensated errors to the initial target location are produced with latencies less than the average latency of saccades on trials with no target step. Noncompensated saccades to the initial target location are followed by corrective saccades to the final target location following an intersaccade interval that decreases with the interval between the target step and the initiation of the noncompensated saccade. We show that this pattern of results cannot be accounted for by a race between two stochastically independent processes producing the saccade to the initial target location and another process producing the saccade to the final target location. However, performance can be accounted for by a race between three stochastically independent processes--a GO process producing the saccade to the initial target location, a STOP process interrupting that GO process, and another GO process producing the saccade to the final target location. Furthermore, if the STOP process and second GO process start at the same time, then the model can account for the incidence and latency of mid-flight corrections and rapid corrective saccades. This model provides a computational account of saccade production when the image changes unexpectedly.

Using spatial terms to select an object.

Our interactions with the world often involve selecting one object from a cluttered array of objects. One way to accomplish this is with language. For example, spatial terms, such as above, guide selection by specifying the position of one object (the located object) with respect to a second object (the reference object). Most of the work on the apprehension of spatial terms has examined displays that contain only these two objects. In the present paper, we examine how the presence of an extra object (a distractor) in the display impacts apprehension. Consistent effects of distractor presence were obtained across acceptability-rating and speeded sentence/picture verification tasks. Importantly, these effects were independent of the placement of the distractor. These results suggest that the distractor has its influence during processes that spatially index and identify the located and reference objects and that processes involved in computing the spatial term operate only on these objects.

Parallel memory retrieval in dual-task situations: II. Episodic memory.

Three experiments asked whether subjects could retrieve information from a 2nd stimulus while they retrieved information from a 1st stimulus. Subjects performed recognition judgments on each of 2 words that followed each other by 0, 250, and 1,000 ms (Experiment 1) or 0 and 300 ms (Experiments 2 and 3). In each experiment, reaction time to both stimuli was faster when the 2 stimuli were both targets (on the study list) or both lures (not on the study list) than when 1 was a target and the other was a lure. Each experiment found priming from the 2nd stimulus to the 1st when both stimuli were targets. Reaction time to the 1st stimulus was faster when the 2 targets came from the same memory structure at study (columns in Experiment 1; pairs in Experiment 2; sentences in Experiment 3) than when they came from different structures. This priming is inconsistent with discrete serial retrieval and consistent with parallel retrieval.

The ecological validity of delay aversion and response inhibition as measures of impulsivity in AD/HD: a supplement to the NIMH multimodal treatment study of AD/HD.

Impulsivity is a primary symptom of the combined type of Attention Deficit/Hyperactivity Disorder (AD/HD). The Stop Signal Paradigm is premised upon a primary deficit in inhibitory control in AD/HD, whereas the Delay Aversion Hypothesis, by contrast, conceptualizes impulsivity in AD/HD, not as an inability to inhibit a response, but rather as a choice to avoid delay. This study compared the ecological validity of the Stop Signal Task (SST) and Choice-Delay Task (C-DT) measure of delay aversion, with respect to their relative utility in discriminating AD/HD children from normal control participants, and their correlations with classroom observations and with ratings of impulsivity and other core AD/HD symptoms on the Conners and SNAP-IV checklists. The tasks exhibited modest discriminant validity when used individually and excellent discriminant validity when used in combination. The C-DT correlated with teacher ratings of impulsivity, hyperactivity, and conduct problems, and with observations of gross motor activity, physical aggression, and an AD/HD composite score. The SST correlated with the observations only. These results suggest that delay aversion is associated with a broad range of AD/HD characteristics whereas inhibitory failure seems to tap a more discrete dimension of executive control.

Executive control of visual attention in dual-task situations.

A theory of executive control is presented that proposes that executive processes control subordinate processes by manipulating their parameters, reconfiguring them to respond in accord with the current task set. It adopts C. Bundesen's (1990) theory of visual attention (TVA) and R. M. Nosofsky and T. J. Palmeri's (1997) exemplar-based random walk (EBRW) as the theory of subordinate processes. It assumes that a task set is a set of TVA and EBRW parameters sufficient to perform a task and that set switching involves changing those parameters. The theory solves 2 computational problems that emerge in dual-task situations: the binding problem and the serial order problem. It can perform dual tasks in series or in parallel but prefers the serial strategy because it is faster and it solves the binding problem naturally. The theory accounts for concurrence cost, set-switching cost, crosstalk between tasks, and the modulation of crosstalk by task set.

Supporting communication in rehabilitation engineering teams.

The objectives of this project were to examine how members of a colocated rehabilitation engineering team communicate during their work and hence deduce the implications of these communications for the design of video-based technologies to support communication among members of a virtual rehabilitation engineering team. Twenty-four assessment clinic sessions conducted by rehabilitation engineering team were recorded on videotape over a period of 3 years. These tapes were analyzed in considerable detail using a schema to identify and classify the talk and actions of the team members. Combining talk and actions with artifacts is a mechanism used by designers to develop ideas and communicate them to others. Speakers rely on actions to support and make their talk lucid. Cooperation based on sharing artifacts is a strength of face-to-face interaction. Participants can experience artifacts and observe others using the artifacts. Tools such as videoconferencing to support virtual rehabilitation teams will have to provide the participants with the ability to see often quite subtle gestures and actions if they are to grasp the meaning of the talk. Increased understanding how a team communicates visually complex data may (1) aid development of next generation videoconferencing equipment to better support distributed designers and rehabilitation engineers and (2) guide development of techniques to enhance the quality of visual data presentation in current videoconferencing systems.

Parallel memory retrieval in dual-task situations: I. Semantic memory.

Can participants retrieve information about the 2nd of 2 stimuli while they are processing the 1st? Four experiments suggest they can. Reaction times to the 1st stimulus were faster if it came from the same category as the 2nd than if it came from a different category. This category-match effect was observed for letter-digit discrimination (Experiment 1), magnitude and parity judgments about digits (Experiment 2), and lexical decisions (Experiment 3). Experiment 4 showed that the 2nd stimulus could semantically prime the 1st. The category-match effect was observed only when the same task was performed on the 2 stimuli. When the task changed from the 1st stimulus to the 2nd, there was no advantage of a category match. This dependence on task set may explain previous failures to find parallel retrieval.

Confirmation of an inhibitory control deficit in attention-deficit/hyperactivity disorder.

The objective of this study was to determine whether deficient inhibitory control distinguishes children with a diagnosis of attention-deficit/hyperactivity (ADHD) disorder, conduct disorder (CD), and comorbid ADHD + CD from normally developing children. Participants were rigorously diagnosed children (age 7 to 12 years) with ADHD (N = 72), CD (N = 13) or ADHD + CD (N = 47) and 33 control children (NC). We studied inhibitory control using the stop-signal paradigm, a laboratory task that assessed the ability to inhibit an ongoing action. The ADHD group had significantly impaired inhibitory control compared to NC, CD, and ADHD + CD children. These results indicate that children with ADHD have deficient inhibition as measured in the stop-signal paradigm and that ADHD occurring in the presence of ADHD + CD may represent a phenocopy of CD rather than a variant of ADHD.

Don't look! Don't touch! Inhibitory control of eye and hand movements.

Inhibitory control of eye and hand movements was compared in the stop-signal task. Subjects moved their eyes to the right or left or pressed keys on the right or left in response to visual stimuli. The stimuli were either central (angle brackets pointing left or right) or peripheral (plus signs turning into Xs left or right of fixation), and the task was either pro (respond on the same side as the stimulus) or anti (respond on the opposite side). Occasionally, a stop signal was presented, which instructed subjects to inhibit their responses to the go stimulus. Stop-signal reaction times (SSRTs) were faster overall for eye movements than for hand movements, and they were affected differently by stimulus conditions (central vs. peripheral) and task (pro vs. anti), suggesting that the eyes and hands are inhibited by different processes operating under similar principles (i.e., a race between stop and go processes).

When it hurts to be misled: a Stroop-like effect in a simple addition production task.

In four experiments, subjects saw simple addition equations (e.g., 3 + 4 = 9) and produced the sums while ignoring the presented answer. If the presented answer was false, subjects took longer to produce the sum, as compared with when the presented answer was true (Experiment 1), when there was no answer presented (blanks; Experiment 2), when a letter was presented (Experiment 3), and when a symbol was presented (Experiment 4). The results suggest that subjects were unable to ignore the presented answers, which raises problems for theories of arithmetic verification (i.e., deciding whether 3 + 4 = 9 is true or false) that claim that subjects verify equations by first producing the sum and then comparing the produced sum with the presented answer. Our results are more compatible with theories that claim that in verification and production, an arithmetic knowledge base is used in different ways.

Judgments of perceptual groups: reliability and sensitivity to stimulus transformation.

The reliability of subjects' judgments of the groups present in dot patterns and the sensitivity of those judgments to stimulus transformation were assessed. The subjects indicated the groups that they saw within random dot patterns, and each judgment was compared with those of other subjects and with their own judgments for related presentations. Within subjects, each pattern appeared in an initial presentation, an identical repetition, and a transformed state (a rotation or a change in scale). Within-subjects judgments were more reliable than between-subjects judgments. An interpretation of within-subjects results was made in relation to predictions made by a formal algorithm of grouping by proximity (the CODE algorithm), which assumes that grouping by proximity is invariant over transformations such as rotations or changes in scale. A slight cost to transforming the patterns was found. The implications for CODE and for using grouping judgments as data are discussed.

Development of inhibitory control across the life span.

The stop-signal procedure was used to examine the development of inhibitory control. A group of 275 participants, 6 to 81 years of age, performed a visual choice reaction time (go) task and attempted to inhibit their responses to the go task when they heard a stop signal. Reaction times to the stop and go signals were used to assess performance in inhibition and response execution, respectively. Results indicated the speed of stopping becomes faster with increasing age throughout childhood, with limited evidence of slowing across adulthood. By contrast, strong evidence was obtained for age-related speeding of go-signal reaction time throughout childhood, followed by marked slowing throughout adulthood. Hierarchical regression confirmed that the age-related change in inhibitory control could not be explained by general speeding or slowing of responses. Findings are discussed in regard to the contrast between the development of inhibition and response execution and the utility of the stop-signal procedure.

What is learned during automatization? II. Obligatory encoding of spatial location.

Six experiments addressed the encoding of location information during automatization, to test a critical prediction of the instance theory of automaticity (G. D. Logan, 1988). Subjects searched 1- or 2-word displays for members of a target category. Specific targets appeared in the same locations consistently throughout training, and then location changed at transfer. Sensitivity to changes in location were assessed with implicit and explicit memory tests. In both tests, sensitivity depended on the number of locations the words could occupy (2 vs. 16). Sensitivity varied with the number of words presented (1 vs. 2) in the implicit test, but not in the explicit test. The results suggest that subjects encoded the locations of the words during automatization, which confirms the predictions of the instance theory.

Decomposing visual search: evidence of multiple item-specific skills.

Four experiments demonstrated that visual search can be decomposed into two components: one consisting of skills shared with memory search and the other consisting of skills not shared with memory search. A training-transfer paradigm was used to test for transfer from memory search to visual search and vice versa. When the same targets and distractors were used in training and transfer, visual search practice completely trained memory search, but memory search practice only partially trained visual search. Learning on both the shared and the private components of visual search benefited more from item-specific training than from nonspecific training. The relationship between the components and some theorized models of visual search are discussed, particularly in terms of prioritization learning.

Response inhibition in AD/HD, CD, comorbid AD/HD + CD, anxious, and control children: a meta-analysis of studies with the stop task.

The aim of this study was to investigate whether impaired response inhibition is uniquely related to AD/HD or whether deficits in response inhibition are also evident in other psychopathological disorders. Furthermore, the suggestion was examined that anxiety disorders are associated with abnormally high levels of response inhibition. This paper presents the results of a meta-analysis of eight studies in which response inhibition was assessed with the so-called stop task in five groups of children: children with attention deficit/hyperactivity disorder (AD/HD), children with conduct disorder (CD), children with AD/HD + CD, children with anxiety disorders, and control children. A total of 456 children participated in the 8 studies. All children were in the age range 6-12 years. Consistent and robust evidence was found for a response inhibition deficit in AD/HD. However, response inhibition deficits did not distinguish children with AD/HD from children with CD, nor from children with comorbid AD/HD + CD. Contrary to predictions, anxious children did not demonstrate enhanced levels of response inhibition.

What is the mechanism for fluency in successive recognition?

There are a number of reasons to believe that processing fluency may affect successive recognition judgements, but evidence about the mechanism for these effects is currently lacking. This study used a successive task design to examine whether subjective ease might underlie effects of fluency on recognition. At study subjects performed lexical decisions; in a subsequent test with studied and new items, subjects performed lexical decisions followed immediately by recognition or ease judgments. In a previous study we used that process dissociation procedure to show that recognition in a similar task was largely based upon fluency. In the present study, successive recognition judgments interfered with lexical decision performance to a greater degree than did ease judgments, suggesting that the recognition judgment was not automatic and involved processes additional to the judgment of ease. The data suggest that the fluency involved in successive recognition is more complex than a subjective judgment of ease of processing. One possible mechanism for fluency in recognition may be based upon reductions in the orientation of attention that accompany item repetition.

Process dissociation, cognitive architecture, and response time: comments on Lindsay and Jacoby (1994)

Process dissociation is based on 2 assumptions about the processes being dissociated: invariance of the processes across situations, and stochastic independence of the processes. In a recent application of process dissociation to the Stroop task (D. S. Lindsay & L. L. Jacoby, 1994), both of those assumptions were violated. It is argued that these violations were due to (a) an oversimplification of the processing architecture that ignores common stages such as guessing and response selection, (b) an assumption that the more automatic process (word reading) dominates over the intended process (color naming) in determining responses, and (c) an assumption that switching from the more common speeded response instruction (measuring speed) to a deadline response instruction (measuring accuracy) does not change processing. General implications for applying process dissociation to dynamic tasks are discussed.

Potential for use of a House of Quality Matrix technique in rehabilitation engineering.

This article describes a concept of using the House of Quality matrix tool to aid the process of designing customized seating. The work of a cross-function team in two seating clinics was videotaped. At a later date the information derived from the videotapes was analyzed using a House of Quality matrix. We were interested in the capacity of House of Quality to draw out customer requirements in a seating device and relate engineering requirements for manufacturing the seating. The scores for engineering features derived from the matrix were compared with the features the cross-function team treated with high priority and also the features which the team experienced most difficulty in satisfying as revealed in the video viewed. The matrix scores demonstrated the House of Quality's capacity to select key features 50% of the time. House of Quality was time-consuming to execute. Its application in everyday clinical settings is limited by this fact.

The role of attention in automatization: does attention operate at encoding, or retrieval, or both?

In this research, we investigated whether attention operates in the encoding of automatized information, the retrieval of automatized information, or in both cases. Subjects searched two-word displays for members of a target category in focused-attention or divided-attention conditions that were crossed with block (training vs. transfer). To see whether subjects encoded all available items or only attended items, we compared performance for subjects in different training conditions but in the same transfer condition. Subjects encoded attended items. To see whether subjects retrieved all the items they had in memory, or only items associated with that to which they were attending at retrieval, we compared performance for subjects in the same training conditions but in different transfer conditions. Subjects retrieved attended items. Attention was found to operate at both encoding and retrieval. These findings support the instance theory of automaticity, which predicts the role of attention at encoding and retrieval.