Effects of time and event uncertainty upon sequential information processing

Two experiments were conducted to investigate the psychological refractory period (PRP), a delay induced into the second of two reaction times (RT) when the interstimulus interval (ISI) is short. In Experiment1, time and event uncertainty were factorially varied by providing or not providing S with foreknowledge of the ISI and the order in which the two events would occur, respectively. ISIs of0, 50, 100, 200, and400 msec were used. Time and event uncertainty produced independent degradation of both RTs. Also, the second RT (RT ₂ ) was delayed at50 msec ISI when both time and event certainty were present. Experiment 2 attempted to replicate this latter finding using ISIs of0, 25, 50, 75, and100 msec. Delays in RT ₂ were found for the middle three values of ISI. These results were interpreted as supporting a modified single channel theory of the PRP.     

Providing a sensory basis for models of visual information acquisition

Our major goal is to account for some simple digit-recall data with a theory that integrates two models from two scientific traditions. Therandom-sampling model, founded in the memory and attention literature, holds that (1) stimulus features are randomly sampled throughout the course of stimulus presence and (2) proportion correct recall is equal to the ratio of sampled features to total features.The linear-filter model, founded in the vision and sensation literature, holds that the initial stages of the visual system act as a low-pass temporal filter on the input stimulus, resulting in a time-varyingsensory response in the nervous system. We report two experiments in which a variable-duration, masked, four-digit string had to be immediately recalled. Experiment 1 was designed principally to replicate past data confirming the basic random-sampling model. Like others, we were able to confirm the model only by endowing it with an additionalprocessing-delay assumption: that feature sampling does not begin until the stimulus has been physically present for some minimal duration. Experiment 2 was an extension of Experiment 1 in which the target stimulus was preceded, 250 msec prior to its onset, by a 50-msec pre-presentation ofthe same stimulus called aprime. The Experiment 2 results allowed the following conclusions. First, the initial processing delay found in Experiment 1 is immutably tied to stimulus onset; that is, if there are two stimulus onsets, separated even briefly in time, there are two associated processing delays. Second, processing rate is essentially unaffected by the prime’s presentation. Third, being presented with a 50-msec prime is equivalent, in terms of memory performance, to increasing unprimed stimulus duration by approximately 30 msec; the prime can thus said to beworth 30 msec of additional exposure duration. This third conclusion seems superficially paradoxical, in the sense that one would expect that having seen a 50-msec prime would be equivalent to increasing exposure duration byat least the same 50 msec. However, both the initial processing delays and the 30-msec prime’s worth are natural consequences of our theory that conjoins the random-sampling model with the linear-filter model.     

Intersensory effects in the psychological refractory period

Two experiments examined reaction time (RT) to each of two stimulus events separated by short interstimulus intervals (1SI). The essential contrast was RT to the second visual signal, RT₂, in auditory-visual (A-V) vs visual-visual (V-V) sequences. With response, certain pairings in Experiment 1, an effect apparently demonstrating a single-channel process (Welford, 1952), was noted. RT₂ was generally faster for A-V as opposed to V-V sequences especially when Ss were uncertain as to the sequence that would occur. At 0-msec ISI, the RT₂ difference between sequences approached the RT! difference. More rapid RT₂ to A-V sequences was also observed with go vs no-go pairings in Experiment 2 when the initial event was a go signal. However, the RT difference disappeared upon error correction, making the RT₂ sequence difference of questionable relevance to the hypothetical single-channel process. RT₂ was more rapid following a null no-go signal when the no-go signal was contrasted with a visual as opposed to auditory go signal. The latter effect was independent of error and is consistent with channel-switching theory (Kristofferson, 1967).     

Hick’s law equivalent for reaction time to individual stimuli

Hick’s law, one of the few law-like relationships involving human performance, expresses choice reaction time as a linear function of the mutual information between the stimulus and response events. However, since this law was first proposed in 1952, its validity has been challenged by the fact that it only holds for the overall reaction time (RT) across all the stimuli, and does not hold for the reaction time (RT_i) for each individual stimulus. This paper introduces a new formulation in which RT_i is a linear function of (1) the mutual information between the event that stimulus i occurs and the set of all potential response events and (2) the overall mutual information for all stimuli and responses. Then Hick’s law for RT follows as the weighted mean of each side of the RT_i equation using the stimulus probabilities as the weights. The new RT_i equation incorporates the important speed–accuracy trade-off characteristic. When the performance is error-free, RT_i becomes a linear function of two entropies as measures of stimulus uncertainty or unexpectancy. Reanalysis of empirical data from a variety of sources provide support for the new law-like relationship.     

Auditory apparent motion in the free field: The effects of stimulus duration and separation

The effects of stimulus duration and spatial separation on the illusion of apparent motion in the auditory modality were examined. Two narrow-band noise sources (40 dB, A-weighted) were presented through speakers separated in space by 2.5°, 5°, or 100, centered about the subject’s midline. The duration of each stimulus was 5, 10, or 50 msec. On each trial, the sound pair was temporally separated by 1 of 10 interstimulus onset intervals (ISOIs): 0, 2, 4, 6, 8, 10, 15, 20, 50, or 70 msec. Five subjects were tested in nine trial blocks; each block represented a particular spatial-separation-duration combination. Within a trial block, each ISOI was presented 30 times each, in random order. Subjects were instructed to listen to the stimulus sequence and classify their perception of the sound into one of five categories: single sound, simultaneous sounds, continuous motion, broken motion, or successive sounds. Each subject was also required to identify the location of the first-occurring stimulus (left or right). The percentage of continuous-motion responses was significantly affected by the ISOI [F(9,36) = 5.67,p < .001], the duration × ISOI interaction [F(18,72) = 3.54,p < .0001], and the separation × duration × ISOI interaction [F(36,144) = 1.51,p < .05]. The results indicate that a minimum duration is required for the perception of auditory apparent motion. Little or no motion was reported at durations of 10 msec or less. At a duration of 50 msec, motion was reported most often for ISOIs of 20–50 msec. The effect of separation appeared to be limited to durations and-ISOIs during which little motion was perceived.     

Visual masking effects on duration,size, and form discrimination

In duration, size, and form discrimination tasks, a visual noise mask was presented at variable delays after stimulus offset in order to interrupt processing and control the extent of processing time. Previous work (Thomas & Cantor, 1975) had suggested that both perceived duration and perceived nontemporal “information” might be expected to increase as processing time was extended. As predicted, accuracy in the discrimination of size of circles and form of non-sense figures was found to vary directly with stimulus duration (20, 50 msec) and mask delay interval (0, 30, 70, 110 msec). Differences in perceived duration between filled (forms or circles) and unfilled (blank) intervals were found to increase monotonically with increases in the mask delay interval, when non-sense forms, but not circles, were presented. Two hypotheses of visual masking (“integration” and “interruption”) are discussed. Within the context of the “integration” hypothesis, a model is proposed which predicts processing time as a function of stimulus duration, mask delay interval, and the interval between onset of the mask and termination of processing.     

Tests of a two-stage model of visual matching

Predictions from a model of visual matching were tested in two experiments. The model consists of a wholistic comparison process followed by an element-by-element comparison process. All stimuli are processed by the first stage but only those that permit a decision based on a wholistic comparison produce responses. When discrimination is difficult and a decision cannot be reached by a wholistic comparison, the second stage of processing is initiated. Degree of discriminability and stimulus duration (100 and 1000 msec.) were varied in both experiments. In Exp. 1, the stimulus elements were arranged in a square configuration to facilitate a wholistic comparison. As predicted, the hard-different stimuli took longer to match than the same or easy-different stimuli. The hard-different stimuli presented for 1000 msec. took longer to match than those presented for 100 msec. There was no difference in accuracy between responses to hard-different pairs at the two durations. In Exp. 2, the stimulus elements were arranged in a horizontal row and placed one above the other to facilitate element-by-element comparison. As predicted, these stimuli produced slower and more accurate responses for same and hard-different stimulus pairs only when they were exposed for 1000 msec. Responses to easy-different stimulus pairs were made quickly and accurately.     

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.     

The effect of frequency variation upon RT to the second of two shortly spaced auditory stimuli

A prepulse of a duration of 25 msec (S₁) was followed by an auditory reaction stimulus (S₂) requiring a binary choice.     

Effects of exposure duration and eccentricity of global and local information on processing dominance

Abstract

The effects of exposure duration of stimuli and the eccentricity of local and global information in hierarchical patterns on processing dominance were examined using a paradigm of selective attention and masked stimuli. In the first experiment, the aim was to determine whether the exposure duration of stimuli has differential effects on processing dominance. Stimuli were presented with spatial certainty and controlled eccentricity at four exposure durations (unlimited, 140 msec, 70 msec and 40 msec). The results showed global advantage independently of the exposure duration used. Differential effects were obtained in relation to the interference between the global and local levels depending on the exposure duration. The purpose of the second and third experiments was to determine whether the eccentricity of local and global levels affects processing dominance under a condition of brief exposure duration of stimuli. The results of Experiment 2 showed local dominance when the eccentricity was different for both levels and biased to the local level (H's and S's stimuli). On the contrary, they showed global dominance when the eccentricity of the two levels was the same (C's stimuli). The results of Experiment 3 revealed that the effect of global dominance persisted when the stimuli presented local and global information foveally.     

Immediate and delayed recognition of sequentially presented random shapes.

Two experiments tested whether short-term memory accounts for the recency effect observed with rapid sequential presentation of nonverbal stimuli. Four random shapes were presented sequentially (with no interstimulus interval) on each trial at rates of 150 msec, 250 msec, 500 msec, and 1,000 msec per stimulus. Subsequent recognition varied positively with exposure duration, ranging from 57% at 150 msec to 77% at 1,000 msec. Two serial position effects were observed: a slight decrease in recognition accuracy for the first stimulus in each sequence and a large increase in recognition for the last stimulus in each sequence. The recency effect was not altered by an intervening 30-sec delay, an intervening 30-sec copying task, or an intervening 30-sec copying and counting task. Since neither visual nor verbal distractors altered recognition accuracy, it was suggested that all shapes were processed directly into long-term memory storage. It also was hypothesized that long-term storage of a nonverbal stimulus requires identification of a distinctive feature of the stimulus and that this process may continue for a brief period after actual stimulus offset.     

Inhibition of return: A graphical meta-analysis of its time course and an empirical test of its temporal and spatial properties

Immediately after a stimulus appears in the visual field, there is often a short period of facilitated processing of stimuli at or near this location. This period is followed by one in which processing is impaired, rather than facilitated. This impairment has been termed inhibition of return (IOR). In the present study, the time course of this phenomenon was examined in two ways. (1) A graphical metaanalysis plotted the size of the effect as a function of the stimulus onset asynchrony (SOA) of the two stimuli. This analysis showed that IOR is impressively stable for SOAs of 300-1,600 msec. It also showed that the literature does not provide any clear sense of the duration of IOR. (2) An empirical approach was, therefore, taken to fill this gap in our knowledge of IOR. In three experiments, IOR was tested using SOAs between 600 and 4,200 msec. IOR was robust for approximately 3 sec and appeared to taper off after this point; the observed duration varied somewhat as a function of the testing conditions. In addition, for the first second, the degree of inhibition was inversely related to distance of the target from the original stimulus, but for the next 2 sec this spatial distribution was not observed. Theories of the mechanisms and function of IOR must conform to these spatial and temporal properties.     

Subjective shortening in humans' memory for stimulus duration

Three experiments investigated memory for stimulus duration in humans using a modification of a delayed-matching technique previously used to study event memory in pigeons. In a session of 48 discrete trials subjects were presented with a sample stimulus (a 500-Hz tone with mean duration of 400 msec) then a comparison stimulus (the same duration as the sample, or longer or shorter), after a delay that was 1 to 10 sec in Experiments 1 and 2, and 2 to 16 sec in Experiment 3. After the comparison had been presented, subjects judged whether the sample and comparison had the same duration (a YES/NO decision, Experiment 1), or whether the comparison was longer, shorter, or of the same duration as the sample (Experiments 2 and 3). Overall, mean number of correct responses changed little with increases in the delay, but the change of number of correct responses with delay was markedly different on trials in which the sample and comparison were the same, the comparison was shorter, or the comparison was longer. In general, accuracy declined with increasing delay in the first case, remained constant in the second case, and increased when the comparison was longer than the sample. Examination of the types of errors made on the different sorts of trials (Experiment 3) suggested that the data were produced by two mechanisms: (1) subjective shortening of the sample as the delay between sample and comparison increased, and (2) a time-order error to respond that the sample was longer than the comparison. Overall, it appears that humans' working memory for duration exhibits a subjective shortening effect similar to that previously found in pigeons.     

Effects of Number of Alternatives on the Psychological Refractoriness of an Extended Movement,

The single-channel prediction that delays in RT₂ should be proportional to RT₁ was examined by varying the number of alternatives (one, two, or three) in the primary response which was an extended arm swing at maximal speed. The second response was a thumb key release. Foreperiods were 2, 3, or 4 sec., and interstimulus intervals (ISIs) ranged from .10:50 sec. in .10-sec. steps. General support for the single-channel model was found in that RT₂ paralleled changes in RT₁. However, RT₂ was greater than predicted when the second signal (S₂) occurred during the execution of the primary response. In addition, while delays in RT₂ as a function of ISI – RT₁ showed corresponding differences between choice conditions, most values were greater than predicted. The deviations from the single-channel model appeared to be explained best in terms of a decrease in readiness to respond to the second signal as ISI lengthened.     

Reaction time to the second of two shortly spaced auditory signals both varying in intensity

Six subjects participated in a reaction time (RT) task in which the stimulus events consisted of two sinusoidal waves presented in close succession. The leading stimulus (S₁) had a duration of 25 msec while the binary reaction stimulus (S₂) was 250 msec. Presentation of the interstimulus interval (ISI) was irregular. S₁ as well as S₂ varied in intensity and were assigned randomly the values of 45, 68, 85 and 105 db (SPL). RT to S₂ was examined as a function of the intensity of both stimuli. Generally RT varied inversely with the intensity of S₁ and the downward gradient of RT with ISI became steepened at least for ISIs shorter than 200–250 msec. Concerning S₂, RT grew shorter as the intensity increased up to 85 db. Probably due to startle, RT tended to lengthen at S₂ = 105 db. When both S₁ and S₂ were 105 db the startle effect upon RT seemed most evident. Then the elevation in RT took place at especially those ISIs for which he fastest RTs might have been expected (about 200 msec). For the remaining intensities no interaction between S₁ and S₂ upon RT was found even for the shortest ISIs, implying that the effects of S₁ and S₂ intensities upon RT were independent.     

Abrupt changes in visual stimulation enhance processing of form and location information

Two experiments investigated the role that abrupt changes in stimulation play in the processing of visual information. In both experiments, the prestimulus field contained a linear array of alternating characters and the target field contained a single target character in one of the positions of the prestimulus array. The target character was either identical to the character in the prestimulus array in that position (no-form change) or was a different character (form change). In the first experiment, the duration of the prestimulus array was 500 msec, and judgments about both the target’s form and location were found to be more accurate in the form-change condition. In the second experiment, the duration of the prestimulus array was varied from 10 to 320 msec. A general decrease was found in performance (in both form and location judgments) as the duration of the prestimulus array was increased. The detrimental effect of increasing the duration of the prestimulus array was larger for no-form-change than for form-change trials. These results are accounted for by a quantitative model that assumes that a stimulus onset initiates a brief period of rapid information processing, followed by a period with reduced rate of processing.     

Processing demands of sequential information

Three experiments examined the processing capacity required to use sequential information in a serial reaction time task with partially predictable sequences. The first two experiments varied the response stimulus interval (RSI) between 0 and 500 msec and found the relative advantage of the high-probability stimulus to be independent of the length of the RSI. The third experiment compared utilization of sequential information either with or without a secondary task. The secondary task did not affect the high-probability stimulus but did increase the amount of time required to respond to the low-probability events. The results are discussed in terms of the attentional demands of memory access.     

Cholinergic modulation of visual attention and working memory: dissociable effects of basal forebrain 192-IgG-saporin lesions and intraprefrontal infusions of scopolamine

Two experiments examined the effects of reductions in cortical cholinergic function on performance of a novel task that allowed for the simultaneous assessment of attention to a visual stimulus and memory for that stimulus over a variable delay within the same test session. In the first experiment, infusions of the muscarinic receptor antagonist scopolamine into the medial prefrontal cortex (mPFC) produced many omissions but did not impair rats' ability to correctly detect a brief visual stimulus. However, these animals were highly impaired in remembering the location of that stimulus following a delay period, although in a delay-independent manner. In the second experiment, another group of animals with selective 192IgG-saporin lesions of the nucleus basalis magnocellularis (nBM) were not impaired under conditions of low-attentional demand. However, when the stimulus duration was reduced, a significant memory impairment was observed, but similar to the results of the first experiment, the nBM-lesioned animals were not impaired in attentional accuracy, although aspects of attention were compromised (e.g., omissions). These findings demonstrate that (1) cortical cholinergic depletion produces dissociable deficits in attention and memory, depending on the task demands, (2) delay-independent mnemonic deficits produced by scopolamine are probably due to impairments other than simple inattention, and (3) working memory deficits are not simply dependent on attentional difficulties per se. Together, these findings implicate the nBM cortical cholinergic system in both attentional and mnemonic processing.     

Semantic and translation priming from a first language to a second and back: Making sense of the findings

The present study investigated cross-language priming effects with unique noncognate translation pairs. Unbalanced Dutch (first language [L1])-English (second language [L2]) bilinguals performed a lexical decision task in a masked priming paradigm. The results of two experiments showed significant translation priming from L1 to L2 (meisje-GIRL) and from L2 to L1 (girl-MEISJE), using two different stimulus onset asynchronies (SOAs) (250 and 100 msec). Although translation priming from L1 to L2 was significantly stronger than priming from L2 to L1, the latter was significant as well. Two further experiments with the same word targets showed significant cross-language semantic priming in both directions ( jongen [boy]-GIRL; boy-MEISJE [GIRL]) and for both SOAs. These data suggest that L1 and L2 are represented by means of a similar lexico-semantic architecture in which L2 words are also able to rapidly activate semantic information, although to a lesser extent than L1 words are able to. This is consistent with models assuming quantitative rather than qualitative differences between L1 and L2 representations.     

Aptitude-related differences in auditory information processing: effects of selective attention and tone duration

College students selected for high or low aptitude performed an auditory backward recognition masking task in which tones differed in pitch (770 or 870 Hz) and duration (10, 13 or 20 msec). Ss were required to attend selectively to the pitch but not to the duration of the targets. As predicted, higher aptitude was associated with lower recognition thresholds at all tone durations. Although increased attentional demands impaired recognition thresholds, this had no apparent differential effect on aptitude-related differences in auditory information processing.