Parallel and serial search in haptics

We propose a model that distinguishes between parallel and serial search in haptics. To test this model, participants performed three haptic search experiments in which a target and distractors were presented to their fingertips. The participants indicated a target's presence by lifting the corresponding finger, or its absence by lifting all fingers. In one experiment, the target was a cross and the distractors were circles. In another, the target was a vertical line and the distractors were horizontal lines. In both cases, we found a serial search pattern. In a final experiment, the target was a horizontal line and the distractors were surfaces without any contours. In this case, we found a parallel search pattern. We conclude that the model can describe our data very well.     

Effect of template complexity on visual search and dual-task performance

Even dissimilar tasks interfere with one another when done together. We used visual search to examine the underlying cause of such interference. In many models, visual search is a process of biased competition controlled by a template describing the target to be sought. When the display is processed, matching against this template guides attention to the target. We show that increasing template complexity increased interference with a dissimilar concurrent task, story memory. This result was independent of reaction time: Increases in template complexity were associated with no increase in search time in Experiment 1 and with a decrease in search time in Experiment 2. The results show that the dual-task demands of visual search reflect the complexity of the template used in task control, and that this factor can be isolated from other sources of difficulty.     

Implications of search accuracy for serial self-terminating models of search

In two experiments, the data from a total of 35 participants was compared to predictions from two competing serial search models, one with perfect memory and one with no memory. Reaction times were collected from an unlimited exposure duration, 4-alternative, target identification search task with array sizes of 8, 12, or 16 items. From the linear function relating RT to number of distractors a hypothetical “inspection time/item” was computed under the assumption of SSTS. Target identification accuracy was obtained from the same participants using the same displays, but with pre- and post-masks used to limit total inspection time (to 120, 180, 300, and 540 ms). Neither the memoryful nor memoryless model provided a good enough fit to the data to support the assumption that serial inspection is the primary process determining search time. Despite direct evidence for serial allocation of attention in visual search, these results suggest that scholars should seriously consider the possibility of hybrid search models in which serial and parallel strategies operate jointly.     

Parallel and serial processes in visual search

A long-standing issue in the study of how people acquire visual information centers around the scheduling and deployment of attentional resources: Is the process serial, or is it parallel? A substantial empirical effort has been dedicated to resolving this issue (e.g., J. M. Wolfe, 1998a, 1998b). However, the results remain largely inconclusive because the methodologies that have historically been used cannot make the necessary distinctions (J. Palmer, 1995; J. T. Townsend, 1972, 1974, 1990). In this article, the authors develop a rigorous procedure for deciding the scheduling problem in visual search by making improvements in both search methodology and data interpretation. The search method, originally used by A. H. C. van der Heijden (1975), generalizes the traditional single-target methodology by permitting multiple targets. Reaction times and error rates from 29 representative search studies were analyzed using Monte Carlo simulation. Parallel and serial models of attention were defined by coupling the appropriate sequential sampling algorithms to realistic constraints on decision making. The authors found that although most searches are conducted by a parallel limited-capacity process, there is a distinguishable search class that is serial.     

Visual search time based on stochastic serial and parallel processings

Two stochastic latency models were developed in order to account for random fluctuations of the search time that the S consumed when he was asked to search for a single target number or one of two (or three) target numbers through the sets of small two-digit numbers randomly distributed on a white square. It was shown that the search time distribution for a single target number can be adequately described in terms of McGill’s two-step serial processing model. The parallel processing model whose structure is exponential was found to fit approximately the search time distributions for the first target number that the S detects among the two (or three) target numbers predesignated. This model, however, does not satisfactorily handle the long search times.     

Chlorpromazine and serial reaction performance

The effect of 25 mg or 75 mg of chlorpromazine on the serial reaction performance of 12 male human subjects was studied. Speed or number of correct responses was reduced by the high dose of chlorpromazine and errors of commission and omission were increased. The adverse effect of the drug upon speed appeared only at the end of the half-hour test. By contrast the adverse effect upon gaps and errors was apparent throughout the test and there was no interaction with test duration.     

Tinnitus and short-term serial recall in stable versus intermittent masking conditions

The relation between tinnitus and short-term memory performance in varying background sounds is not well understood. In the present study a sample of 18 persons with tinnitus completed a serial recall test in three conditions, silence, masking and intermittent masking. The performance of a matched control group without tinnitus was also investigated. Based on the literature on the "irrelevant sound effect" we expected that the tinnitus group would perform worse during intermittent masking and that they would score lower overall compared to the control group. Results revealed no statistically significant differences between the groups, nor any group interaction within sound conditions for the serial recall test. Groups did however differ regarding subjective measures of concentration problems, anxiety and depression. Results are discussed in relation to thought suppression and distraction from tinnitus.     

Electrophysiological evidence for parallel and serial processing during visual search

Event-related potentials were recorded from young adults during a visual search task in order to evaluate parallel and serial models of visual processing in the context of Treisman's feature integration theory. Parallel and serial search strategies were produced by the use of feature-present and feature-absent targets, respectively. In the feature-absent condition, the slopes of the functions relating reaction time and latency of the P3 component to set size were essentially identical, indicating that the longer reaction times observed for larger set sizes can be accounted for solely by changes in stimulus identification and classification time, rather than changes in post-perceptual processing stages. In addition, the amplitude of the P3 wave on target-present trials in this condition increased with set size and was greater when the preceding trial contained a target, whereas P3 activity was minimal on target-absent trials. These effects are consistent with the serial self-terminating search model and appear to contradict parallel processing accounts of attention-demanding visual search performance, at least for a subset of search paradigms. Differences in ERP scalp distributions further suggested that different physiological processes are utilized for the detection of feature presence and absence.     

Effects of secondary tasks on search performance

Summary Two experiments studied the effect of secondary task load on continuous visual search. Two effects were observed when a secondary task was applied. Search speed (which is assumed to reflect the efficiency of nontarget rejection) was impaired, whereas target detection distance (which presumably reflects the efficiency of target detection) increased. These findings are explained in the framework of a two-process model of visual search which assumes that two operations are performed simultaneously during each fixation, that is, automatic detection and controlled search. The secondary task interferes with the operation of controlled search which reacts to this impairment by way of a compensatory slow-down of search speed. This gain in time also benefits the operation of automatic detection which converts the temporal gain into a spatial extension of the area under its control.     

Variability and noise in continuous force production

In the present 3 experiments, the authors examined the hypothesis, derived from information theory, that increases in the variability of motor responses result from increases in perceptual-motor noise. Three different groups of participants (Ns = 10, 9, and 10, respectively, in Experiments 1, 2, and 3) produced continuous isometric force under either low, intermediate, or high target force levels. When considered together, the results showed that force variability (SD) increased exponentially as a function of force level. However, an index of information transmission (M/SD), as well as measures of noise in both the time (approximate entropy) and the frequency (power spectrum) domains, changed according to an inverted-U-shaped function over the range of force levels. The findings provide further evidence that increased information transmission is related to increases, and not to decreases, in the noisiness of the structure of force output.