Effects of intramodal and crossmodal stimulus diversity on the reaction time of chronic schizophrenics.

Compared 16 chronic schizophrenics (mean age 42.7 yrs), 16 alcoholic inpatients (mean age 37.6 yrs), and 16 healthy Ss (mean age 36.9 yrs) with respect to their RTs to stimuli from 1 (ipsimodal condition) or 2 (crossmodal condition) modalities. In the ipsimodal condition, a low-pitched sound presented to one ear and a high-pitched sound presented to the other ear served as imperative stimuli, alternating randomly. In the crossmodal condition, a light or a sound was presented. In responding to the sound imperative stimuli, schizophrenics were more retarded than were comparison groups when the preceding imperative stimulus was a light or a different sound, relative to when it was the same sound. With the inclusion of warning stimuli of either modality into the crossmodal condition, both comparison groups were more retarded than were schizophrenics when the preceding imperative stimulus was a light, relative to when it was the same sound. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence of preliminary response preparation from a divided attention task.

In a divided attention situation, preliminary response activations produced by stimuli on one channel were revealed through their effects on responses to stimuli on a secondary probe channel. Subjects performed concurrent but independent four-choice reaction-time tasks using the same four response fingers (middle and index fingers on both hands). In the main task, targets were large and small Ss and Ts, and medium-sized Ss and Ts sometimes appeared as distractors. Targets in the probe task were squares differing in location. A response to a probe square was faster if a distractor letter presented just before it had the same name as the target letter corresponding to that square (i.e., assigned to the same response key) than if the distractor letter had a different name—a result indicating that distractor letters cause partial response preparation. The timecourse of the effect demonstrated that preparation was based on preliminary information about distractor name that was available before distractor size had been determined. The results support models in which response preparation can sometimes begin before stimulus recognition has finished. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

P300 from a single-stimulus paradigm: auditory intensity and tone frequency effects

The P300 component of the event-related brain potential (ERP) was elicited with auditory stimuli in two different tasks. The oddball paradigm presented both target and standard stimuli; the single-stimulus paradigm presented a target but no standard tone stimulus, with the inter-target interval the same as that for the oddball condition. Experiment 1 manipulated stimulus intensity and Experiment 2 manipulated tone stimulus frequency, with the relative target probability maintained 0.20 for both tasks. P300 amplitude and latency were highly similar for the oddball and single-stimulus procedures in both experiments across independent variables. The findings suggest that the single-stimulus paradigm may prove useful in experimental and applied contexts that require very simple ERP task conditions.     

Components of the location probability effect in visual search tasks.

In visual search tasks, targets are detected more rapidly when they appear in locations that commonly contain a target than when they appear in locations that rarely contain a target. Five experiments were conducted to investigate 2 specific properties of this location probability effect. In Exp I spatial location of a stimulus row was varied to determine whether high location probability facilitates target detection in a particular location in visual space or a particular relative position within the row. Both were facilitated to approximately the same extent. In Exp II an inducing target occurred with high probability in 1 of 4 display locations, and a test target occurred with equal probability in all 4 locations. Both targets were found more quickly in the high-probability location than in the other locations, but the advantage associated with targets in the high-probability location was larger for the inducing target than for the test target. In Exps III–V the correspondence between the components observed in Exps I and II was examined. The overall pattern of results was compatible with a model in which the location probability effect is produced partly by an attentional spotlight, which facilitates processing of any stimulus appearing in a particular location in visual space, and partly by a network of position-specific letter detectors, which facilitates detection of a particular letter in a particular relative position within a display. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. Ss performed recognition judgments on each of 2 words that followed each other by 0, 250, and 1,000 msec (Experiment 1) or 0 and 300 msec (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 lst 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 l; 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amphetamine and the adenosine A2A antagonist KW-6002 enhance the effects of conditional temporal probability of a stimulus in rats.

As the length of foreperiod preceding an imperative signal increases, reaction time decreases and anticipatory (prior to the signal) responding increases. The authors designed a task to dissociate the effect of elapsing time in the foreperiod and conditional temporal probability of the imperative stimulus. The effects of 2 drugs--amphetamine and KW-6002--known to enhance the effect of foreperiod were compared. Three groups of rats were trained to respond to an auditory signal presented at 1 of 3 foreperiods, unpredictable from trial to trial. The length of preparation time was different for each group, but conditional temporal probability was the same. Reaction times were faster as a function of increased preparation time, whereas anticipatory responses were strongly modulated by conditional probability. Both amphetamine and KW-6002 speeded reaction times and increased anticipatory responding. The pattern of behavior was consistent with the suggestion that they enhanced the motor preparatory effects of conditional probability rather than speeded a timing process. The authors concluded that preparation time and expectancy (conditional temporal probability of an imperative signal) have differential effects on performance and that amphetamine and KW-6002 enhance the effect of expectancy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How does feature-based attention affect visual processing?

Five experiments are reported from which it is concluded that attending on the basis of a stimulus feature (e.g., red) does not directly affect the sensory quality of stimuli that possess that feature. Feature-based attention was manipulated in a visual search task by providing information about the probability that the target would possess a given feature (e.g., "The target has a 1.0 probability of being red when present.") Feature-based attention failed to aid performance under "data-limited" conditions (i.e., those under which performance was primarily affected by the quality of the stimulus) but did affect performance under conditions that were not data limited (Experiments 1-3). If attending to a feature had affected the sensory quality of stimuli, performance should have been aided under all conditions. Experiments 4 and 5 provided converging support for this conclusion.     

Effects of structural and naming factors of letters upon the recognition of tachistoscopic letters (author''s transl)

To determine the nature of effects of a preceding letter stimulus upon the recognition of a following letter stimulus, 20 subjects were sequentially and tachistoscopically presented pairs of letters of pairs of random patterns, which consist of the same number of elements, and asked to judge whether they were "same" or "different" in form. Four variable interstimulus intervals (ISI) between the 1st stimuli and the 2nd stimuli were employed as parameters. Results obtained were as follows: (a) percentages of correct responses for the letters were not significantly different from those for the random patterns, and (b) percentages of correct responses for the "same" matching tasks were significantly higher than those for the "different" matching tasks, but, differences in number of correct responses between the two tasks diminished as ISI increased. These results reveal structural, rather than naming, effects of preceding letters in the information processing of matching single letters.     

Event-related potentials associated with covert orientation of visual attention in Parkinson's disease

Event-related potentials (ERPs) were measured in a group of patients with idiopathic Parkinson's disease and compared with a matched control group during a task involving covert orientation of visual attention. Central warning cues directed attention to the probable location of a lateralized signal that required a button-press response. Parkinson patients had enhanced post-cue P1 (at Oz) and P2 (at Cz) amplitudes, delayed N1 (at Oz) latencies, and diminished CNV amplitudes. Post-target amplitudes were similar to controls, except for an enhanced P1 to invalidly cued targets, and delayed N1 and P3 target latencies. These results indicate that Parkinson patients, in addition to their motor deficits, process spatial cues more effortfully and slowly, have impaired response preparation, and process imperative stimuli more slowly.     

Intentional and Unintentional Contributions to Nonspecific Preparation: Electrophysiological Evidence.

The authors hypothesized that there are distinct intentional and unintentional influences on nonspecific preparation for a future event. In 2 experiments, participants responded to an imperative stimulus (S?) that was presented equiprobably either 400 ms or 1,200 ms after the offset of a warning stimulus (S?). During the S?-S? interval, the authors measured the contingent negative variation (CNV), an event-related brain potential reflecting nonspecific preparation. S? provided either no information or reliable information about the duration of the impending S?-S? interval, thereby allowing an intentional influence on the state of preparation. The effect of S? information on the CNV was approximately additive to the effect of the S?-S? interval that was used on the preceding trial. This supports the view that the preceding S?-S? interval contributes unintentionally to the state of nonspecific preparation guided by a process of trace conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of bilateral stimulation and stimulus redundancy on interhemispheric interaction.

Recent visual laterality studies have included trials in which critical stimulus information is presented simultaneously in both visual half-fields and, thereby, simultaneously to both cerebral hemispheres. To investigate interhemispheric interaction, researchers compare performance on bilateral redundant trials with performance on unilateral trials in which a single copy of the target is presented to one hemisphere or the other. The authors used the identification of nonword letter trigrams to examine the relationship between unilateral and bilateral performance when the 2 types of trials were equated for the number of locations stimulated (Experiment 1) and the number of redundant copies of the target (Experiment 2). Results suggest that when the number of stimulated locations is held constant, each of 2 copies of a target stimulus can be processed with the same efficiency and the same strategy as it would have been had it been the only copy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Action planning in the presence of distracting stimuli: An investigation into the time course of distractor effects.

Humans have a remarkable capability to respond efficiently to a stimulus of interest despite other stimuli competing for neural resources. The current study investigated how the human system copes with distracting stimuli. During each trial, participants viewed 2 sequential stimuli that were each associated with a specific action based on an arbitrary mapping. The 1st stimulus served as a distractor, and the 2nd stimulus required a response (target). When the distractor preceded the target by more than a few hundred milliseconds, response latencies were slower when the 2 stimuli were associated with the same response. The authors propose that this negative compatibility effect stemmed from an inhibitory mechanism that the human system utilizes to prevent the distractor from eliciting an unwanted response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Foreperiod and simple reaction time.

Reviews studies of simple visual and auditory reaction processes published since W. H. Teicher (1954), with emphasis on the preparatory phase of these processes, particularly the foreperiod (FP). The 1st section consists of the analysis of actual FP variables; duration, regularity, range, distribution, and preceding FPs. The 2nd section deals with factors affecting the relation between FP and reaction time (RT): (a) the modality, intensity, probability, and duration of the warning signal and reaction stimulus (RS) and (b) the speed–accuracy trade-off. It is suggested that the S's expectancy (momentary probability of the immediate delivery of the RS) is the most important determinant of the preparation to respond to the RS at any moment during a trial and, hence, of RT. Many factors exert their influence on preparation through their effect on expectancy. Other factors have a direct influence on preparation: short-term exhaustion and fatigue, immediate arousal evoked by intense auditory stimuli, the S's stimulus criterion, the speed–accuracy trade-off, and fluctuation in motor preparedness owing to inaccuracies in the control of motor preparation. (4? p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cessation and persistence of wife assault: a longitudinal analysis

The effects of stimulus duration and prior task experience on gaze shift were studied to determine the spatial characteristics of gaze shift as affected by prior experience. Thirty-six subjects (with normal or corrected-to-normal vision) participated in two sessions of a task that required viewing two consecutively presented letters at either 15 degrees or 50 degrees eccentricity and deciding whether they were the same or different. In the first session (SS1) a letter was presented for either 500 (N = 18) or 1000 ms (N = 18), followed by a second letter. In session 2 (SS2), the groups were divided with half of the group performing the task under the same conditions as they did in SS1, while the other half was switched to the other first letter duration. Head and eye movements were recorded using a photoelectric transducer and electrooculogram (EOG), respectively. Few head movements occurred with targets presented at 15 degrees eccentricity. Approximately 80% of gaze shifts to the 50 degrees stimuli included a head movement component. DURATION had a significant effect on gaze shift. Head movement amplitude (HMA) increased, while saccade amplitude decreased with an increase in DURATION. On the average, the proportion of gaze shift accomplished via head movement was 24% if DURATION was 500 ms, and 37% when DURATION was extended to 1000 ms. SS1 task experience affected HMA in SS2. When DURATIONs differed between SS1 and SS2, HMA in SS2 were drawn toward the level of HMA in SS1. A positive and significant correlation was observed between head movement amplitude and head movement duration. The results suggest that both stimulus availability and prior experience affect head movement amplitude in gaze shift.     

The role of physical and conceptual properties in preserving object continuity.

Six experiments investigated the nature of the object-file representation supporting object continuity. Participants viewed preview displays consisting of 2 stimuli (either line drawings or words) presented within square frames, followed by a target display consisting of a single stimulus (either a word or a picture) presented within 1 of the frames. The relationship between the target and preview stimuli was manipulated. The first 2 experiments found that participants responded more quickly when the target was identical to the preview stimulus in the same frame (object-specific priming). In Experiments 3, 4, 5, and 6, the physical form of the target stimulus (a word or picture in 1 frame) was changed completely from that of either preview stimulus (pictures or words in both frames). Despite this physical change, object-specific priming was observed. It is suggested that object files encode postcategorical information, rather than precise physical information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The disappearance of foveal and nonfoveal stimuli: Decomposing the gap effect.

When a foveal stimulus disappears prior to the appearance of a peripheral target, saccadic reaction times (RTs) are reduced. The present study, with 6 undergraduates, compared this gap effect for foveal and nonfoveal stimuli when a highly predictive auditory warning signal was or was not presented. Without a tone, there was a gap effect for both foveal and nonfoveal stimuli; with a tone, there was a gap effect for foveal but not for nonfoveal stimuli. Highly predictive warning tones also modulated the gap effect in a manner that seemed to reflect top-down release of ocular inhibition. It is argued that the gap effect therefore consists of 3 components: (1) warning effects; (2) release of ocular inhibition due to the disappearance of a foveal stimulus; and (3) release of ocular inhibition due to top-down processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interhemispheric Interaction in Bilateral Redundancy Gain: Effects of Stimulus Format.

Previous visual laterality experiments have shown that identification is better when 2 copies of the same stimulus are presented--1 to each hemisphere--than when only a single copy is presented to 1 hemisphere. New experiments were conducted to vary whether the 2 stimuli on a bilaterally redundant trial were physically identical or identical in format in addition to leading to identical responses. Substantial bihemispheric gain was obtained even when the 2 stimuli were perceptually distinctive (e.g., letter trigrams differing in case and font or the same numeric quantity represented by digits and dots). Thus, much of the bihemispheric advantage involves relatively abstract aspects of information processing. However, when the formats were sufficiently distinctive, there were small effects on bihemispheric performance, suggesting some role for less abstract processes that are sensitive to physical characteristics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The gap effect during visual and auditory stimulation using manual responses

Six experiments were conducted in naive human participants to examine any facilitation produced in manual reaction time (RT) by the interposition of a temporal gap between a warning signal and an imperative signal. Peripheral visual stimuli and monoaural auditory stimuli were used as targets. Participants showed a facilitation of RTs to the targets for both auditory and visual stimuli in the five experiments in which RTs were the dependent variable. In addition, the gap effect increased over successive blocks of trials, suggesting learning. RTs were facilitated only when the gap had predictive value and was salient. Using a variable temporal gap or visual warning stimulus did not change the facilitation in RTs. A further experiment demonstrated that the gap can be perceived by the participants. The dissociation between a learned and a non-learned component in the gap effect suggests that the temporal gap induces two independent processes: warning and disengagement of attention.     

What is learned about nontarget items in simple visual search?

Human sensitivity to correlational structure between nontargets and likelihood of target presence in a visual letter-search task were studied in two experiments. In each of these experiments, the performance of subjects for whom the nontarget information was altered in the final trial block was compared with the performance of subjects for whom the nontarget information did not change. When stimulus strings were presented individually on a computer screen and subjects were required to make a yes-no decision about target presence (Experiment 1), the change in nontarget structure resulted in increased reaction times for target-absent trials. When subjects searched simultaneously for three possible targets (Experiment 2), the change in nontarget structure produced increased error rates and increased reaction times for both target-absent and target-present trials. Correlations between the amount of predictive information in individual stimulus strings and reaction times also showed that both switching and nonswitching subjects were sensitive to the nontarget context. However, neither self-reports of strategy nor postexperiment choices between context-consistent and-inconsistent letter strings indicated any explicit knowledge of the predictive information in the nontarget stimuli. Subjects can thus acquire and benefit from, apparently without awareness, information about subtle correlational structure in nontarget elements in simple visual search.     

Conjunctions of visually based categories: Overextension and compensation.

The degree to which overextension effects found with conjunctions of semantic categories of visual stimuli was tested in 4 experiments. Overextension occurs when participants categorize a stimulus in the conjunction of 2 categories but fail to categorize the same stimulus as belonging to 1 of the 2 constituent categories considered individually. Stimuli for the present experiments were ambiguous colored letter shapes and cartoon faces that could vary along dimensions of happiness and either apparent intelligence or apparent age. Overextension was found with both stimulus sets, thus showing that the phenomenon is not restricted to categorization in superordinate semantic categories. There was also evidence that typicality in 1 category could compensate for borderline membership of the other. More overextension was found for faces than for letters, and there was evidence for asymmetric compensation between category dimensions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)