Speed-accuracy tradeoff in double stimulation: II. Effects on the second response

In the double-stimulation paradigm subjects respond to two successive stimuli. Previous research (Knight & Kantowitz, 1974) showed that a subject's speed-accuracy tradeoff (SAT) strategy interacted with the interval between the two stimuli to determine response performance to the first stimulus. The present experiment examined the influence of SAT strategy on response performance to the second stimulus. Interest focused on effects of SAT strategy upon the psychological refractory period (PRP) effect. If a single mechanism underlies beth first-and second-response performance (e.g., the PRP effect) in double stimulation, effects of SAT upon the second response should be similar to effects upon the first response. Results showed that the PRP effect appeared only when second-response accuracy was stressed. Under speed emphasis double-stimulation second-response latency never exceeded a single-stimulation baseline. This was analogous to first-response latency effects found by Knight and Kantowitz (1974). Response grouping was strongly influenced by SAT strategy and two response-grouping mechanisms were distinguished. Implications of these and interresponse time data for models of double-stimulation performance are discussed.     

Classical and bayesian inference in certain latency processes

Certain aspects of point estimation are treated for two kinds of exponential latency processes. The first unitary process is represented by a simple exponential density in which the rate parameter may be viewed as an unknown constant or as a random variable. If a second, slower exponential process is grafted onto the first, there results a postulated two-component latency between stimulus and response. Moments estimators are derived for the two parameters of this latter density, and the relevance of the second parameter to decision time is emphasized.This research was supported in part by National Institutes of Health Grant MH-04439-05. The author would like to express his appreciation to James Baker of Oregon Research Institute for certain helpful comments concerning aspects of this work.     

Visual persistence as measured by reaction time

Latency of reaction to onset of a visual display was subtracted from latency of reaction to offset. Persistence was defined as difference between the two latency values. Persistence was inversely related to stimulus duration and was comparable for monoptic presentation and for presentation of the first half of the stimulus duration to one eye and the second half to the other. A power function described the relation between persistence and stimulus duration. The possible effects of central intermittency on this type of reaction time measure are discussed.     

Attention to repeated events in human infants (Homo sapiens): effects of joint visual attention versus stimulus change

The goal of this study was to examine the effect of joint visual attention on infants' behavior during subsequent events. Thirty-seven mother-infant (aged from 9 to 13 months) pairs were twice shown a pair of line drawing stimuli on a computer screen. For the control group, the mother never paid attention to the stimuli. For experimental group 1, the mother pointed to one stimulus in the first presentation but did not point to it in the second presentation. The infants gazed longer at the stimulus pointed to by their mothers in the first presentation. In the second presentation, during which mothers did not attend to the stimuli, infants gazed longer at the stimulus which had been pointed to by the mothers in the first presentation. In experimental group 2, one of two stimuli blinked during the first presentation but not the second presentation. Infants gazed for longer at the blinking stimulus in the first presentation, but there was no difference in looking time toward the two stimuli in the second presentation. These results suggest that joint visual attention affects infants' looking behavior during subsequent events, and that simple stimulus change does not. Accepted after revision: 2 May 2001 Electronic Publication     

What determines the eyes’ landing position in words?

The place at which the eyes first fixate in a word during continuous reading, called thepreferred landing position(PLP), is usually located halfway between the beginning and the middle of the word. To propose a mechanism that might account for the off-center location of the PLP, six eye movement experiments were conducted using a lexical decision task (Experiment 1) and a stimulus bisection task (Experiments 2–6). The type of stimulus—linguistic (words and nonwords) versus nonlinguistic (strings of hashes, dotted lines, and solid lines)—and the stimulus presentation side (left vs. right) were manipulated. The results showed that (1) stimulus discreteness versus continuousness is an important factor in saccade computation and (2) PLP asymmetry can be explained in terms of attentional and/or oculomotor processes.     

Control of fixation duration in visual search and memory search: another look

In visual search a variable delay (up to 150 msec) between the beginning of each fixation and the onset of a search stimulus reduces the time (oculomotor latency) between stimulus onset and the subject's next saccadic eye movement. Two hypotheses for this effect of stimulus onset delay (SOD) were compared: first, process monitoring, that SOD simply serves as a warning interval to facilitate saccadic responses; and second, preprogramming, that saccades are preprogrammed at short SODs. In the first experiment SOD produced a decline in oculomotor latency in search similar to that seen in previous studies. In the second and third experiments, the size of the memory set in a Sternberg memory search paradigm was varied, or a mask flanking some of the search stimuli was used, to vary the processing time of each stimulus. Partial preprogramming of saccades at short delays would predict that increasing the processing time of individual stimuli would increase oculomotor latency at only short SODs. However, oculomotor latency increased equally at all SODs. In this search task, then, the SODs appeared to facilitate saccade initiation.     

“Backward masking” of simple detection latencies

Simple detection latencies were determined with stimuli that comprised two successive flashes. The second flash either equaled or exceeded the first in luminance, duration, or both. When a low-luminance flash preceded either a low-or a high-luminance flash, the flashes summated, yielding latencies that were shorter than the latency for the first flash alone. In the limit, when the second flash was intense and followed the first by a short time, the latency for the paired flashes behaved as if it was determined by the second flash alone. This limit was analogous to the retroactive interference in studies of the neurophysiological concomitants of backward masking. However, the S in masking studies detects the first flash despite interference by the second, whereas the present S detected the onset of the stimulus light. The need for an analysis of the S’s response under masking is thus indicated.     

The effects of stimulus movement and attention on peripheral stimulus localization by 8- to 26-week-old infants

This study examined the effect of stimulus movement on localization probability and latency during attention and inattention. Forty infants, 10 each at 8, 14, 20, and 26 weeks of age were presented with a central stimulus. Then, a peripheral stimulus was presented (static or dynamic checkerboard). Stimulus movement did not affect localization probability. Infants localized the dynamic peripheral stimulus more quickly than the static peripheral stimulus when there was no focal stimulus. Focal stimulus attention attenuated this difference in localization latency between static and dynamic stimuli. Signal detection analysis showed that sensitivity to the peripheral stimulus increased over this age range along with a decrease in the bias against responding. The effects of attention were on response bias rather than stimulus sensitivity. These results imply attention affected the localization response to the peripheral stimulus but did not affect the sensitivity of the sensory and perceptual pathways to peripheral stimuli.     

Age effects on a nonverbal auditory sustained attention task

A nonverbal auditory test of sustained attention was administered to 20 young and 20 elderly women, screened to ensure good health. Groups were matched for intelligence. Older subjects performed as accurately as younger subjects. Neither group showed increases in response latency as a function of time spent on test. Older subjects took longer to respond than younger subjects, but only for a particular combination of stimulus duration and order of presenting stimulus durations. When subjects were presented long tones first, there was no difference in response latency associated with age or stimulus duration. When short tones were presented first, older subjects were slower than younger subjects in both duration conditions and in response to long tones were slower than all other subjects.     

Anticipatory attention during the sleep onset period

To examine whether anticipatory attention or expectancy is a cognitive process that is automatic or requires conscious control, we employed a paired-stimulus event-related potential (ERP) paradigm during the transition to sleep. The slow negative ERP wave observed between two successive stimuli, the Contingent Negative Variation (CNV), reflects attention and expectancy to the second stimulus. Thirteen good sleepers were instructed to respond to the second stimulus in a pair during waking sessions. In a non-response paradigm modified for sleep, participants then fell asleep while tones played. As expected, N1 decreased and P2 increased in amplitude systematically with the loss of consciousness at sleep onset; the CNV was increasingly more positive. Sleep onset latency was correlated with the amplitude of the CNV. The systematic attenuation of the CNV waveform at sleep onset and its absence in sleep indicates that anticipatory attention requires endogenous conscious control.     

What determines the eyes' landing position in words?

The place at which the eyes first fixate in a word during continuous reading, called the preferred landing position (PLP), is usually located halfway between the beginning and the middle of the word. To propose a mechanism that might account for the off-center location of the PLP, six eye movement experiments were conducted using a lexical decision task (Experiment 1) and a stimulus bisection task (Experiments 2-6). The type of stimulus--linguistic (words and nonwords) versus nonlinguistic (strings of hashes, dotted lines, and solid lines)--and the stimulus presentation side (left vs. right) were manipulated. The results showed that (1) stimulus discreteness versus continuousness is an important factor in saccade computation and (2) PLP asymmetry can be explained in terms of attentional and/or oculomotor processes.     

Reaction time to a second stimulus as a function of intensity of the first stimulus

Reaction time (RT) to the second of two stimuli presented in rapid succession was examined as a function of the intensity of the first stimulus (S₁). It was found that the delay in RT₂ was greater following a dim first stimulus than following a bright first stimulus. The magnitude of this increase corresponded to the difference in RTs to the two intensity levels of S₁. These results support the prediction of a single channel model of response selection. Examination of mean first RTs revealed a general elevation in latency of RT. However, since this increase was not influenced by the inter-stimulus interval (ISI) or by the intensity of the second stimulus (S₂), and since the same increase was found on “catch trials“ where no S₂ was presented, this increase is considered to be a function of change in set in the double response situation.     

Reaction time and movement time as measures of stimulus evaluation and response processes

Reaction time has been divided into the time to initiate a response (RT) and the time to execute the motor response (MT) in many chronometric studies of intelligence. Our purpose was to determine which cognitive processes are reflected by RT and MT. To accomplish this, the latency of the P300 wave of the event-related potential was recorded concurrently with RT and MT measures in three experiments. P300 latency reflects the duration of stimulus evaluation relatively independently of response processes. In the first experiment, a Sternberg memory task was employed to manipulate stimulus classification requirements. In the second, the subjects' emphasis on either speed or accuracy of responding was examined during a task that also manipulated stimulus evaluation time. In the third experiment, a Stroop-like task was used to examine response processes. RT and P300 latency varied with manipulations of stimulus evaluation time, whereas MT varied with difficulty of motor execution. MT was also affected by stimulus classification processes. Both RT and MT were sensitive to processes involved in response bias and preparation. The possibility that the correlations of RT and MT with measures of intelligence are due to effects on a common stage of information processing cannot be rejected in the light of these results.     

Evidence for split foci of attention in a priming paradigm

Most models of visuospatial attention include the notion that attention is dedicated to a single location in space. However, several researchers have found evidence that under appropriate circumstances, attention may be allocated to noncontiguous locations (e.g., Awh & Pashler, 2000; Bichot, Cave, & Pashler, 1999; Kramer & Hahn, 1995). In the present experiments, the spatial distribution of attention was assessed by a novel method, perceptual latency priming: the latency benefit of an attended visual stimulus, as compared with a nonattended stimulus. Experiment 1 assessed whether observers are able to attend to two nonadjacent regions or a region of variable size. Experiment 2 tested whether, when two distant locations are attended to, the region between them is necessarily also in the focus of attention. Two further experiments controlled for objections against the method used and replicated the main results of the first two experiments. The experiments showed a robust attentional priming effect at two noncontiguous locations of the visual field, simultaneous with little or no priming of the intervening location.     

Speed-accuracy tradeoff in double stimulation: Effects on the first response

A single-stimulation and two double-stimulation response conditions were compared using explicit payoff matrices to vary speed-accuracy tradeoff. Under accuracy payoff, response latency (RT(1)) to the first stimulus increased as ISI dropped but accuracy remained high and relatively constant. Under speed payoff, RT(1) was only slightly affected by ISI but accuracy dropped as ISI decreased. Transmitted information rates consistently reflected detrimental effects of short ISI. In double stimulation, but not in single stimulation, error response latency exceeded correct response latency. Furthermore, error response latencies were found to be far more variable and more sensitive to changes in speed-accuracy condition than were correct response latencies. Finally, under both speed and accuracy conditions, response latency to the first of two successive stimuli was faster if a response was also required to the second stimulus. Implications of the data for possible models of double-stimulation speed-accuracy tradeoff are considered.     

The Effect of Differential Post-Weaning Environment on the Rigidity of an Animal's Behavior

Seventy-two first, second and third grade boys and girls were administered seriation problems involving different combinations of shape and color variation. Success rates and latency scores were influenced by shape variation, but not by color variation or grade level. The failure to obtain predicted interactions between the effects of grade level and stimulus variation was attributed to the clarity of the relevant stimulus dimension.     

Methylphenidate increases selectivity of visual scanning in children referred for hyperactivity

Visual scanning patterns were investigated in 32 children referred for symptoms of hyperactivity in a doubleblind crossover comparison of methylphenidate and placebo treatments. Total errors, response latency, and visual fixations were recorded as the child scanned computer-generated visual matching-to-sample problems. Results indicated that the number of fixations on the standard stimulus in the matching task was significantly larger in the methylphenidate state. Drug treatment also resulted in a significant increase in the number of systematic comparisons between the standard and the variants in the task. However, the increased selectivity of attention to the standard stimulus was not accompanied by a reduction of total errors. It was suggested that the stimulant drug may increase attentional selectivity even when such a shift fails to produce improvement in task performance.This research is based in part upon a master's thesis completed by the first author in the department of Psychology, University of Guelph. The authors are indebted to Dean H. Owen for providing the random polygons used in the experiment. The research was supported by grants from the Ontario Mental Health Foundation and the Medical Research Council of Canada to James M. Swanson.     

How much processing do nonattended stimuli receive? Apparently very little, but...

The early versus late selection issue in attention models was examined by means of a new methodology. Through cues or precues, attention was directed to one location of a multistimulus visual display and, while attention was so engaged, the identity of a stimulus located at a different position in the display was changed. By varying the time after display onset before the stimulus was changed, we controlled the preview time that the original stimulus was represented on the retina. Then, using a marker cue, we directed the subject's attention to the location of the changed stimulus. The subject's response was a timed discrimination between two possible target letters. The data of main interest was the effect of preview time upon the subject's latency in identifying the new target that appeared in the changed location. We found that the preview time of the original stimulus, before RT was affected to the new target, depended upon whether the original stimulus was a neutral (noise) letter or whether it was the alternative target. When the original stimulus was a noise letter, RTs to the new target were just as fast as those obtained in the control condition in which the target was present throughout the preview interval and did not change its identity. Significant effects upon RT were obtained at preview times of 83 msec when the original stimulus was one of the targets that changed to the alternative target. Preview times also varied as a function of precuing. Preview times were correspondingly shortened when the first cue occurred 50 msec before display onset, thus providing an extra 50 msec for attention to be directed to the first display location. The results were interpreted in terms of two separate information-processing systems in the human: an automatic system and an attentional system. Even though a stimulus may have been automatically processed, when the attention system is directed to that stimulus, processing starts at the beginning again.     

Visual attention and temperament: Developmental data from the first 6 months of life

Infants were assessed longitudinally at 2, 4, and 6 months of age on a visual orienting task. Once engaged on a center stimulus, the latency to initiate a saccade to a peripheral stimulus was measured. The critical manipulation was whether, upon presentation of the peripheral stimulus, the center stimulus remained on (disengage trials) or was turned off (shift trials). Temperament was assessed using the Infant Behavior Questionnaire (IBQ). Latencies to shift attention decreased with age (i.e., 6 < 4 < 2 months.). A disengage–shift difference favoring shift trials was found at 2 months; this difference was only marginally significant at 4 and 6 months. At 6 months, ease of disengagement was associated with infants being more likely to smile and less likely to exhibit frustration. Our findings replicate and extend previous cross-sectional research by showing that the disengage operation undergoes a major developmental change within the first 4 months. Discussion focuses on the relationship between attentional disengagement and the regulation of emotional states.     

Attack priming and satiation in female golden hamsters: Tests of some alternatives to the aggression arousal interpretation

“Priming” a female hamster by allowing it a single attack on an intruder placed into its home cage transiently decreases the latency and increases the probability of attack on a second trial. Although we have previously argued that this priming effect reflects an increase in aggressive arousal, an alternative interpretation is that the fear elicited by placing a foreign object into the subject's home cage is reduced when it happens again on the second trial. Another interpretation is that priming is an effect of intruder novelty, i.e., the subject perceives a difference between the first and second intruders which causes it to attack the second more quickly. Experiment 1 compared the standard two trial paradigm with different intruders to trials in which (1) the first intruder was withdrawn and used again in the second trial, and (2) the intruder remained in the cage following the first attack. All intruders were pretreated with the analgesic-sedative methotrimeprazine to reduce the variability of their behavior. Neither hypothesis tested in Experiment 1 was supported, strengthening the interpretation of attack priming as a manipulation that affects primarily internal motivational mechanisms specific to aggression. Allowing a hamster to carry out a protracted series of attacks produces a “satiation” effect that is the reverse of priming, i.e., the latency of a subsequent attack is increased and its probability reduced. It is possible that the attack satiation observed in our earlier studies was not the result of processes internal to the subject, but could have been due to habituation to a particular intruder or to certain stimuli emitted by it during the protracted interaction. In Experiment 2 subjects were given three sessions of 10 successive trials using either 1 intruder presented repeatedly, 2 intruders presented alternately, or 10 different intruders presented once each. No difference among conditions was found in this study either suggesting that subject's aggressive behavior is insensitive to whatever changes may occur in intruders' behavior or other stimulus characteristics when they have been treated with methotrimeprazine. The lack of differences among test conditions in both experiments is most likely due to the efficacy of the drug in “standardizing” intruder behavior. Experiment 2 also revealed an interesting difference in two measures of attack latency. The time elapsing between intruder presentation and attack, i.e., the standard measure of latency, decreased from the first to the fourth trail; it then increased steadily over the remaining trials. The cumulative time that the subject remained in contact with the intruder prior to attack, a measure more indicative of attention to the intruder, dropped to an asymptotic value by the second trial. This difference suggests that the satiation effect may be accounted for by subjects' increasing avoidance of the intruders over trails, perhaps as a way of regualting their level of aggressive arousal.