Impaired temporal discrimination within the attentional blink

Yeshurun and Levy (2003) reported that temporal discrimination performance of a visual stimulus benefits when spatial attention is oriented away from its location. In the present study, we investigated whether this negative influence of attention on temporal discrimination performance is restricted to transient spatial attention or might generalize to other paradigms of attention. We employed the attentional blink (AB) paradigm and required either a spatial (Experiment 1) or a temporal discrimination task (Experiment 2). The results of both experiments revealed a performance decrement if attention was temporally unavailable during the AB and a recovery with increasing attentional availability. Thus, contrary to the results of Yeshurun and Levy, the absence of attention decreased temporal discrimination performance in this paradigm. We hypothesize that attention which operates at different processing levels might exert differential effects on temporal stimulus processing.     

Polydipsia's contribution to temporal discrimination of rats on a fixed interval schedule

This experiment concerned the contribution of polydipsia on the temporal discrimination of rats during a fixed-interval 60-sec. schedule. In this study, the timing accuracy of 12 rats which had access to water during training was compared to that of 12 rats which had no water during training. The rats were trained for 25 sessions on an FI 60-sec. schedule. In early sessions before polydipsia was fully developed, no differences existed between the timing accuracy of the water group and no-water group. As the amount of water drunk by the water group increased as the number of sessions increased, a parallel increase was noted in the timing accuracy of the water group. In the final sessions, a significant difference was found between the timing accuracy of rats in the water group and that of those in the no-water group. It was concluded that polydipsia facilitated the development of the temporal discrimination which is characteristic of a fixed-interval 60-sec. schedule.     

Impaired phonological and orthographic word representations among adult dyslexic readers: evidence from event-related potentials

The authors examined the processing of phonological and orthographic word representations among 17 dyslexic and 16 normal college-level readers using Event-Related Potential measures. They focused on 2 early components--the P200 and the P300. The results revealed P200 and P300 components of lower amplitude and later latency among dyslexic readers than among normal readers for both types of word representation. Group differences were greatest for phonological representations. In addition, the authors observed greater time gaps among dyslexic readers than among normal readers between different processing stages (i.e., between P2 and P3 peaks, between P3 and reaction time). Combined, the data suggest a consistent speed-of-processing deficit among dyslexic readers that is evident within and between stages of cognitive processing. The results are discussed in the context of deficits in stimulus encoding and working memory. In addition, the authors discuss the need for accurate timing and synchronization of phonological and orthographic codes for efficient word recognition.     

Intertrial interval as a contextual stimulus: further analysis of a novel asymmetry in temporal discrimination learning

Four experiments investigated discrimination learning when the duration of the intertrial interval (ITI) signaled whether or not the next conditional stimulus (CS) would be paired with food pellets. Rats received presentations of a 10-s CS separated half the time by long ITIs and half the time by short ITIs. When the long ITI signaled that the CS would be reinforced and the short interval signaled that it would not be (Long+/Short-), rats learned the discrimination readily. However, when the short ITI signaled that the CS would be reinforced and the long interval signaled that it would not (Short+/Long-), discrimination learning was much slower. Experiment 1 compared Long+/Short- and Short+/Long- discrimination learning with 16-min/4-min or 4-min/1-min ITI combinations. Experiment 2 found no evidence that Short+/Long- learning is inferior because the temporal cue corresponding to the short interval is ambiguous. Experiment 3 found no evidence that Short+/Long- learning is poor because the end of a long ITI signals a substantial reduction in delay to the next reinforcer. Long+/Short- learning may be faster than Short+/Long-because elapsing time involves exposure to a sequence of hypothetical stimulus elements (e.g., A then B), and feature-positive discriminations (AB+/A-) are learned quicker than feature-negative discriminations (A+/AB-). Consistent with this view, Experiment 4 found a robust feature-positive effect when sequentially presented CSs played the role of elements A and B.     

Retention interval and intertrial interval in a serial learning or delayed discrimination task

In each of four experiments, rats were provided with the same three-event decreasing series (18-1-0) of 0.045-g food pellets in a runway. Tracking, running fast to 18 pellets and running slow to 1 and 0 pellets, was investigated as a function of the temporal interval elapsing between the events of the series (the retention interval), shifts in retention interval, and number of trials each day (or the intertrial interval), a trial being defined as presentation of each of the three events of the series. Neither retention interval, which varied from 15 s to 30 min in various investigations, nor shifts in retention interval affected tracking when only one trial was given each day. But when more than one daily trial was given, tracking was acquired more slowly and was disrupted by a shift in retention interval from 15 s to 5 min. Tracking was also disrupted by a shift from one to two trials each day. These results indicate that when given one 18-1-0 trial each day, the rat partitions events on a first-event/subsequent-event basis; that little forgetting occurs even at long retention intervals; that somewhat different memories signal events when one or more than one 18-1-0 trial occurs each day; and that retention interval deficits can arise owing to the same or similar memories' signaling different events. The results described limit the generality of three hypotheses suggested in two recent investigations: that as retention interval increases, rats find it increasingly difficult to remember and utilize serial position cues; that tracking in serial tasks is not influenced by number of trials each day; and that there are specific stimuli associated with each retention interval which, when changed, necessarily disrupt performance.     

Joint stimulus control in a temporal discrimination task

The ability to identify stimuli that signal important events is fundamental for an organism to adapt to its environment. In the present paper, we investigated how more than one stimulus could be used jointly to learn a temporal discrimination task. Ten pigeons were exposed to a symbolic matching-to-sample procedure with three durations as samples (2, 6, and 18 s of keylight) and two colors as comparisons (red and green hues). A 30-s intertrial interval (ITI), illuminated with a houselight, separated the trials. Both the houselight and the sample keylight could control responding, so two tests were run to assess how these stimuli influenced choice. In the no-sample test, the keylight was not presented; in the dark-ITI test, the houselight was not illuminated. Results suggest that both houselight and keylight controlled choice, and with the exception of one animal, the more a pigeon relied on one of these stimuli, the less it appeared to rely on the other.     

Errorless learning of a conditional temporal discrimination

In the present study we extended errorless learning to a conditional temporal discrimination. Pigeons' responses to a left-red key after a 2-s sample and to a right-green key after a 10-s sample were reinforced. There were two groups: One learned the discrimination through trial and error and the other through an errorless learning procedure. Then, both groups were presented with three types of tests. First, they were exposed to intermediate durations between 2 s and 10 s, and given a choice between both keys (stimulus generalization test). Second, a delay from 1 s to 16 s was included between the offset of the sample and the onset of the choice keys (delay test). Finally, pigeons learned a new discrimination in which the stimuli were switched (reversal test). Results showed that pigeons from the Errorless group made significantly fewer errors than those in the Trial-and-Error group. Both groups performed similarly during the stimulus generalization test and the reversal test, but results of the delay test suggested that, on long stimulus trials, responding in the errorless training group was less disrupted by delays.     

Intermodal transfer in temporal discrimination

Attention, Perception, & Psychophysics - This study determined if training for accuracy in temporal discrimination would transfer across sensory modalities. A fractionation method was used in...     

Decision processes in temporal discrimination

The processing dynamics underlying temporal decisions and the response times they generate have received little attention in the study of interval timing. In contrast, models of other simple forms of decision making have been extensively investigated using response times, leading to a substantial disconnect between temporal and non-temporal decision theories. An overarching decision-theoretic framework that encompasses existing, non-temporal decision models may, however, account both for interval timing itself and for time-based decision-making. We sought evidence for this framework in the temporal discrimination performance of humans tested on the temporal bisection task. In this task, participants retrospectively categorized experienced stimulus durations as short or long based on their perceived similarity to two, remembered reference durations and were rewarded only for correct categorization of these references. Our analysis of choice proportions and response times suggests that a two-stage, sequential diffusion process, parameterized to maximize earned rewards, can account for salient patterns of bisection performance. The first diffusion stage times intervals by accumulating an endogenously noisy clock signal; the second stage makes decisions about the first-stage temporal representation by accumulating first-stage evidence corrupted by endogenous noise. Reward-maximization requires that the second-stage accumulation rate and starting point be based on the state of the first-stage timer at the end of the stimulus duration, and that estimates of non-decision-related delays should decrease as a function of stimulus duration. Results are in accord with these predictions and thus support an extension of the drift–diffusion model of static decision making to the domain of interval timing and temporal decisions.     

A short intertrial interval facilitates acquisition of context-conditioned fear and a short retention interval facilitates its expression

Rats were shocked in a context on two occasions and then tested for fear reactions as indexed by freezing. Rats spent the interval between conditioning trials and between conditioning and test in their home cages. A short interval between context-conditioning trials or between trials involving a discrete conditioned stimulus (CS) produced better learning than longer intervals. A short retention interval between conditioning and test produced better performance than longer intervals. The effects of the intertrial interval on learning are the opposite of those reported previously and are opposite to those predicted by contemporary learning theories. The effects of the training to test interval on performance are predicted by Wagner's sometimes opponent process (SOP) theory (Wagner, 1981).     

Neuroanatomical and behavioral asymmetry in an adult compensated dyslexic

Individual differences in cortical anatomy are readily observable, but their functional significance for behaviors such as reading is not well understood. Here, we report a case of an apparent compensated dyslexic who had attained high achievement in visuospatial mathematics. Data from a detailed background interview, psychometric testing, divided visual field tasks measuring basic word recognition (word naming, nonword naming, and lexical decision), and more controlled word retrieval (verb, category, and rhyme generation), and measurements of his atypical brain structure are described. The findings suggested that enhanced "top-down" processing could provide the means to compensate for deficient "bottom-up" word decoding skills in this case. Relative to controls, this individual also evidenced unusually large asymmetries on several divided visual field lexical tasks, an extreme leftward asymmetry of the planum temporale, and a rare form of Sylvian fissure morphology (Steinmetz type 4, [Steinmetz, H., Ebeling, U., Huang, Y., & Kahn, T. (1990). Sulcus topography of the parietal opercular region: An anatomic and MR study. Brain and Language, 38, 515-533.]). We suggest that certain forms of brain organization may be associated with successful behavioral compensation for dyslexia, and that anatomical variations in the right hemisphere may be important contributors to individual differences in reading acquisition and achievement.     

Crossmodal temporal order and processing acuity in developmentally dyslexic young adults

We investigated crossmodal temporal performance in processing rapid sequential nonlinguistic events in developmentally dyslexic young adults (ages 20-36 years) and an age- and IQ-matched control group in audiotactile, visuotactile, and audiovisual combinations. Two methods were used for estimating 84% correct temporal acuity thresholds: temporal order judgment (TOJ) and temporal processing acuity (TPA). TPA requires phase difference detection: the judgment of simultaneity/nonsimultaneity of brief stimuli in two parallel, spatially separate triplets. The dyslexic readers' average temporal performance was somewhat poorer in all six comparisons; in audiovisual comparisons the group differences were not statistically significant, however. A principal component analysis indicated that temporal acuity and phonological awareness are related in dyslexic readers. The impairment of temporal input processing seems to be a general correlative feature of dyslexia in children and adults, but the overlap in performance between dyslexic and normal readers suggests that it is not a sufficient reason for developmental reading difficulties.     

Disruption of a temporal discrimination under response-independent shock

The responding of rats was reinforced on one key after a 1-sec auditory stimulus and on a second key after a 5-sec stimulus. With errors punished by a short timeout, all subjects achieved a high level of accuracy. A chain of responses during the stimuli mediated the performance so that when the auditory signals were omitted accuracy decreased only slightly. Response-independent aversive stimulation superimposed upon this procedure both suppressed the total amount of behavior and reduced the accuracy of the discriminative performance, the intensity of the stimulus determining the error rate. The increase in errors under these conditions may have depended in part upon differential suppression of members of the response chain, but such suppression was not necessary, since error rate increased even in its absence. Furthermore, the locus of response disruption within the chain was not consistent from day to day either for any individual animal or across animals.     

The lengthening effect in sequential estimations of a short interval

Summary Experiments were carried out on the lengthening effect in sequential time estimations. It appeared that lengthening only occurred in the case of intuitive evaluation of an interval. Autocorrelation functions revealed that the estimation process may be described as a series of compensatory actions with respect to the last trial. It was assumed that the last estimate is more or less always experienced as too long or too short. In the resulting correction process the positive corrections reach higher mean values than the negative ones since the upper limit of the interval is not defined. In view of the negative autocorrelation in the last trial it was postulated that the correction process is not random, but is related to sequential response bias, i.e. too many alternations. Subsequently, several presentation and estimation modes were compared. The possibility that lengthening might result from trace decay of the standard stored in memory was doubtful since the phenomenon was also observed in the case of pure production on the basis of verbal instructions only. Apparently, it makes no difference whether a standard is presented or not. The distribution of the time estimates under various conditions revealed that the subject becomes more uncertain in proportion as the amount of external reference given increases, so that estimation process variables seem to be of greater importance than stimulus factors (standard presentation). It was assumed that the temporal memory could be described as a register in which only one event (the last) remains available and forms the subject's frame of reference. Since lengthening appeared to be connected with several cognitive variables of a general nature it was postulated that the effect is not only inherent in time estimation, but may be considered as a phenomenon occurring in repeated estimations of various stimuli as well. This assumption appeared to be correct, as analogous effects were observed in the case of repeated line drawing. It was shown that the increase of the time estimates could be influenced significantly by introducing different risk levels, i.e. the degree of lengthening is a function of the subject's decision criterion. Furthermore, there was some correlation between the compensatory actions and sequential response bias in a randomization task. It is concluded that the lengthening effect does not only show a general character, but that it might be described and explained adequately within the framework of the cognitive theory of time experience in which memory mechanisms, decision theory, and sequential response bias play a significant role.     

Electrocortical measures during a lexical decision task: a comparison between elementary school-aged normal and dyslexic readers and adult normal and dyslexic readers

The authors examined the differences in performance between 30 dyslexic readers in 4th grade, 30 dyslexic readers attending university, and age-matched normal readers for both groups on a lexical decision task to evaluate the underlying factors of dyslexia that persist into adulthood. In both age groups, the dyslexic readers were significantly less accurate and slower than were the normal readers when reading word lists and in connected text. Electrophysiological data showed 2 main distinguishing components. Results supported the hypothesis that the dyslexia phenomenon is characterized by inaccurate and slow word-recognition skills. In addition, the authors found slow performance speed among all dyslexic readers in all stages of processing.     

Counting models of temporal discrimination

A three-category task was employed to test counting models for temporal discrimination. Unlike former approaches, the present one is not based on Weber functions. Specifically, the proposed test does not require the implicit but, nevertheless, debatable assumption that the pulse rate of the internal clock is constant for different durations of the standard interval. Furthermore, the present approach does not necessitate specific distributional assumptions about the interpulse times. An experiment was conducted to evaluate the predictions of this generalized counting model. The results are consistent with predictions of the generalized counting model. A further analysis suggests that the pulse rate decreases as the duration of the standard interval increases.     

Variable foreperiods and temporal discrimination

Temporal judgements are often accounted for by a single-clock hypothesis. The output of such a clock is reported to depend on the allocation of attention. In the present series of experiments, the influence of attention on temporal information processing is investigated by systematic variations of the period preceding brief empty intervals to be judged. Two indicators of timing performance, temporal sensitivity, reflecting discrimination performance, and perceived duration served as dependent variables. Foreperiods ranged from 0.3 to 0.6 s in Experiments 1 to 4. When the foreperiod varied randomly from trial to trial, perceived duration was longer with increasing length of foreperiod (Experiments 1 and 3 with brief auditory markers and Experiment 4 with brief visual markers), an effect that disappeared with no trial-to-trial variations (Experiment 2). Longer foreperiods also enhanced performance on temporal discrimination of auditory empty intervals with a base duration of 100 ms (Experiments 1 and 5), whereas discrimination performance was unaffected for auditory intervals with a base duration of 500 ms (Experiment 3). The variable-foreperiod effect on perceived duration also held when foreperiods ranged from 0.6 to 1.5 s (Experiments 5-7). Findings suggest that foreperiods appear to effectively modulate attention mechanisms necessary for temporal information processing. However, alternative explanations such as assimilation or compatibility effects cannot be totally discarded.