Task-evoked Pupillary Responses Research Articles

Frequency analysis of a task-evoked pupillary response: Luminance-independent measure of mental effort

Pupil diameter is a widely-studied cognitive load measure, which, despite its convenience for non-intrusive operator state monitoring in complex environments, is still not available for in situ measurements because of numerous methodological limitations. The most important of these limitations is the influence of pupillary light reflex. Hence, there is the need of providing a pupil-based cognitive load measure that is independent of light conditions. In this paper, we present a promising technique of pupillary signal analysis resulting in luminance-independent measure of mental effort that could be used in real-time without a priori on luminous conditions. Twenty-two participants performed a short-term memory task under different screen luminance conditions. Our results showed that the amplitude of pupillary dilation due to load on memory was luminance-dependent with higher amplitude corresponding to lower-luminance condition. Furthermore, our experimentation showed that load on memory and luminance factors express themselves differently according to frequency. Therefore, as our statistical analysis revealed, the ratio between low (0–1.6Hz) and high frequency (1.6–4Hz) bands (LF/HF ratio) of power spectral densities of pupillary signal is sensitive to the cognitive load but not to luminance. Our results are promising for the measurement of load on memory in ecological settings.

Pupillary Dynamics Reveal Computational Cost in Sentence Planning

This study investigated the computational cost associated with grammatical planning in sentence production. We measured people's pupillary responses as they produced spoken descriptions of depicted events. We manipulated the syntactic structure of the target by training subjects to use different types of sentences following a colour cue. The results showed higher increase in pupil size for the production of passive and object dislocated sentences than for active canonical subject-verb-object sentences, indicating that more cognitive effort is associated with more complex noncanonical thematic order. We also manipulated the time at which the cue that triggered structure-building processes was presented. Differential increase in pupil diameter for more complex sentences was shown to rise earlier as the colour cue was presented earlier, suggesting that the observed pupillary changes are due to differential demands in relatively independent structure-building processes during grammatical planning. Task-evoked pupillary responses provide a reliable measure to study the cognitive processes involved in sentence production.

Effects of arousal on cognitive control: empirical tests of the conflict-modulated Hebbian-learning hypothesis

An increasing number of empirical phenomena that were previously interpreted as a result of cognitive control, turn out to reflect (in part) simple associative-learning effects. A prime example is the proportion congruency effect, the finding that interference effects (such as the Stroop effect) decrease as the proportion of incongruent stimuli increases. While this was previously regarded as strong evidence for a global conflict monitoring-cognitive control loop, recent evidence has shown that the proportion congruency effect is largely item-specific and hence must be due to associative learning. The goal of our research was to test a recent hypothesis about the mechanism underlying such associative-learning effects, the conflict-modulated Hebbian-learning hypothesis, which proposes that the effect of conflict on associative learning is mediated by phasic arousal responses. In Experiment 1, we examined in detail the relationship between the item-specific proportion congruency effect and an autonomic measure of phasic arousal: task-evoked pupillary responses. In Experiment 2, we used a task-irrelevant phasic arousal manipulation and examined the effect on item-specific learning of incongruent stimulus–response associations. The results provide little evidence for the conflict-modulated Hebbian-learning hypothesis, which requires additional empirical support to remain tenable.

Human intention recognition based on eyeball movement pattern and pupil size variation

To develop an efficient nonverbal human computer interaction system it is important to interpret the user's implicit intention, which is vague. According to cognitive visuo-motor theory, the human eye movements are a rich source of information about the human intention and behavior. According to Beatty's study, a task-evoked pupillary response is a consistent index of the human cognitive load and attention. In this paper, we propose a novel approach for a human's implicit intention recognition based on the eyeball movement pattern and pupil size variation. Based on the Bernard's research, we classify the human's implicit intention during a visual stimulus as informational and navigational intent. In the present study, the navigational intent refers to the human's idea to find some interesting objects in a visual input without a particular goal while the informational intent refers to the human's aspiration to find a particular object of interest. The proposed model utilizes the salient features of the eye such as fixation length, fixation count and pupil size variation as the inputs to classify the human's implicit intention. The experimental results show that the proposed model can achieve plausible recognition performance.

Task-evoked pupillary responses in iconic memory

Introduction: Task-evoked pupillary responses (TEPR) are a reliable measure of cognitive effort (Beatty, 1982). They vary systematically with working memory load (Kahneman & Beatty, 1966), up to a ceiling, when working memory capacity is reached (Granholm, et al., 1996). Our aim was to investigate whether the same pattern holds for in iconic memory. Methods: In each trial, five expert observers were presented with a set of differently-colored star-shaped items, spaced symmetrically around central fixation. Trials were blocked by set size, with either 4, 6, 8, or 10 items presented. After a 1000 ms exposure, a randomly chosen pair of neighboring items disappeared; this amounts to a zero-latency partial report post-cue. After 500 ms, the two items reappeared, with one changed to a new color and the other unchanged. Participants were instructed to look at the item that changed. Eye movements and pupil diameters were collected throughout the trial by a Tobii T120 eye tracker. Results and conclusions: When set size is below iconic memory capacity, performance on this task should be maximal. As set size exceeds capacity, performance should drop. Indeed, performance was near ceiling for up to 6 items, then started to decrease, pointing to a capacity of 6 items (see Blaser & Kaldy, 2010). However, unlike load-dependent TEPRs that were found in the working memory literature, TEPRs in this task did not increase with set size. In addition to this, there were no significant differences in TEPR between correct and incorrect trials (in set size 10), indicating that errors were caused by failures of memory retrieval, not effort. In short, increasing the load on iconic memory does not result in a concomitant pupil increase, suggesting that these increasing demands do not draw on the same set of cognitive resources demanded by working memory. Meeting abstract presented at VSS 2013

Task-evoked pupillary responses in iconic memory

Task-evoked pupillary responses in iconic memory

Pupil Dilation Co-Varies with Memory Strength of Individual Traces in a Delayed Response Paired-Associate Task

Studies on cognitive effort have shown that pupil dilation is a reliable indicator of memory load. However, it is conceivable that there are other sources of effort involved in memory that also affect pupil dilation. One of these is the ease with which an item can be retrieved from memory. Here, we present the results of an experiment in which we studied the way in which pupil dilation acts as an online marker for memory processing during the retrieval of paired associates while reducing confounds associated with motor responses. Paired associates were categorized into sets containing either 4 or 7 items. After learning the paired associates once, pupil dilation was measured during the presentation of the retrieval cue during four repetitions of each set. Memory strength was operationalized as the number of repetitions (frequency) and set-size, since having more items per set results in a lower average recency. Dilation decreased with increased memory strength, supporting the hypothesis that the amplitude of the evoked pupillary response correlates positively with retrieval effort. Thus, while many studies have shown that “memory load” influences pupil dilation, our results indicate that the task-evoked pupillary response is also sensitive to the experimentally manipulated memory strength of individual items. As these effects were observed well before the response had been given, this study also suggests that pupil dilation can be used to assess an item’s memory strength without requiring an overt response.

Method for Characterizing and Identifying Task Evoked Pupillary Responses During Varying Workload Levels

Abstract : Understanding when operators are experiencing high workload is important in the design and implementation of Command, Control, Communications, Computers, Intelligence, Surveillance and Reconnaissance (C4ISR) systems. Fortunately physiological metrics, such as pupillary reflexes, have been shown to correlate with increases in mental workload. This paper proposes an automated method for characterizing and identifying task evoked pupillary responses (TEPR) during various workload levels. This method captures findings and observations from previous TEPR studies in an automated algorithm. This algorithm characterizes the rate of pupil dilation and constriction into a TEPR area metric, which is then used to identify times of increased operator workload. Independent trial analysis shows the benefits of using the TEPR area for distinguishing different workload responses but additional investigation is needed to make the algorithm more robust to individual variability.

Cognitive load in simultaneous interpreting: Model meets data

Seeber (2011) recently introduced a series of analytical cognitive load models, providing a detailed illustration of conjectured cognitive resource allocation during simultaneous interpreting. In this article, the authors set out to compare these models with data gathered in an experiment using task-evoked pupillary responses to measure online cognitive load during simultaneous interpreting when embedded in single-sentence context and discourse context. Verb-final and verb-initial constructions were analysed in terms of the load they cause to an inherently capacity-limited system when interpreted simultaneously into a verb-initial language like English. The results show larger pupil dilation with verb-final than with verb-initial constructions, suggesting higher cognitive load with asymmetrical structures. A tendency for reduced cognitive load in the discourse context compared to the sentence context was also found. These data support the models’ prediction of an increase in cognitive load towards (and beyond) the end of verb-final constructions.

Resource allocation and fluid intelligence: Insights from pupillometry

Thinking is biological work and involves the allocation of cognitive resources. The aim of this study was to investigate the impact of fluid intelligence on the allocation of cognitive resources while one is processing low-level and high-level cognitive tasks. Individuals with high versus average fluid intelligence performed low-level choice reaction time tasks and high-level geometric analogy tasks. We combined behavioral measures to examine speed and accuracy of processing with pupillary measures that indicate resource allocation. Individuals with high fluid intelligence processed the low-level choice reaction time tasks faster than normal controls. The task-evoked pupillary responses did not differ between groups. Furthermore, individuals with high fluid intelligence processed the high-level geometric analogies faster, more accurately, and showed greater pupil dilations than normal controls. This was only true, however, for the most difficult analogy tasks. In addition, individuals with high fluid intelligence showed greater preexperimental pupil baseline diameters than normal controls. These results indicate that individuals with high fluid intelligence have more resources available and thus can solve more demanding tasks. Moreover, high fluid intelligence appears to be accompanied by more task-free exploration.

Detecting phasic lapses in alertness using pupillometric measures

Small, nonreflexive pupillary changes are robust physiological indicators of cognitive activity. In the present paper, we examined whether measures of pupillary changes could be used to detect phasic lapses in alertness during a vigilance task. A polynomial curve-fitting method for quantifying parameters from single task-evoked pupillary responses (TEPRs) is described. The TEPR parameters associated with long latency responses (indicating low alertness) were compared to the TEPR parameters associated with normal latency responses (indicating an alert state) within a multilevel modeling framework. Three parameters, pupil diameter, linear pupil dilation rate and curvilinear pupil dilation rate, significantly differed between the long latency and normal latency response types. The results provide preliminary evidence that these parameters would be useful neurocognitive markers of operator state in a bio-behavioral alertness monitoring system.

Effects of incentive on working memory capacity: Behavioral and pupillometric data

We evaluated the hypothesis that individual differences in working memory capacity are explained by variation in mental effort, persons with low capacity exerting less effort than persons with high capacity. Groups previously rated high and low in working memory capacity performed the reading span task under three levels of incentive. The effort hypothesis holds that low span subjects exert less effort during task performance than do high spans. Subjects' pupil sizes were recorded online during task performance as a measure of mental effort. Both recall performance and pupil diameter were found to be increased under incentives, but were additive with span (incentives increased performance and pupil diameter equivalently for both span groups). Contrary to the effort hypothesis, task-evoked pupillary responses indicated that if anything, low span subjects exert more effort than do high spans.

Pupillometric indices of temporal order representation in semantic memory

Summary. The present study used the technique of pupillometry to study whether pupillary changes are sensitive to variations in the processing of temporal order information in semantic memory. By employing two recognition tasks the temporal orientation (chronological vs. reverse) between pre-information and target was manipulated. The first experiment examined frequently occurring sequences of everyday events (e.g., cut - bleed - bandage) with the same strength of temporal relatedness for preceding and succeeding events. The second experiment investigated event-feature pairs (e.g., melt, solid - fluid) with temporal connectives (before, after). In addition to the psychological indicators reaction times and error rates two further psychophysiological indicators - maximum pupil diameters and dilatation times - were raised to validate the behavioral data. The results show that time’s arrow is not restricted to sequences of events, but also embedded in the mental representation of individual events. In both experiments psychophysiological indicators coincide with the psychological indicators. The pupillometric results provide additional new information: They indicate that the processing of temporal orientation towards future time does not only consume less time and produces less errors, but also that the processing is making less demands on mental resources. The presented study demonstrates that task-evoked pupillary response is a reliable and sensitive indicator for the experimental study of cognitive load.

Pupillary responses and processing resources on the visual backward masking task

Task-evoked pupillary responses were recorded during a visual backward masking task as an index of resource allocation. Increased pupillary dilation indicates increased allocation of processing resources to the task. Consistent with numerous studies, detection accuracy increased with longer interstimulus intervals and approximated no-mask accuracy in the 300-ms condition. Pupillary dilation responses were significantly greater during task performance (cognitive load) than during a passive stimulus viewing condition (no-load) and were significantly greater in the 300-ms condition than the no-mask condition. Consistent with models of early visual information processing, the results suggest that the mask demanded extra processing resources when it followed the target by more than 100 ms. Pupillography methods may be useful in evaluating the contribution and timing of resource-demanding processes during early visual information processing.

Eye tracking impairment in clinically identified patients with schizotypal personality disorder

Eye tracking accuracy, which has been found to be impaired in schizophrenic patients and their relatives, was assessed in 26 patients with schizotypal personality disorder, 17 control subjects with other non-schizophrenia-related personality disorders, 29 normal control subjects, and 44 schizophrenic patients. Both schizotypal and schizophrenic patients, but not control subjects with other personality disorders, demonstrated significantly more impaired tracking than the normal control subjects. These results suggest that patients with clinically defined schizotypal personality disorder may be biologically related to schizophrenic patients as part of a spectrum of schizophrenia-related disorders.

The pupil and stimulus probability.

ABSTRACTThree studies were conducted to examine the relationship of the task‐evoked pupillary response (TEPR) to the probability of the eliciting stimuli in Bernoulli sequences. Subjects counted target tones in sequences containing two types of tones differing in pitch. For a given probability level, both targets and non‐targets elicited pupillary dilations that were similar in amplitude. The dilation to both targets and non‐targets was inversely related to probability at low probability levels. This relationship appeared to break down at high probability levels, at least for non‐targets. When tone omissions were used as targets they elicited a larger dilation than tonal targets at very low target probability. The amplitude of dilations produced by omitted targets was also affected by probability. The data converge to indicate that the TEPR in random stimulus sequences is sensitive to the surprise value of events, whether involving a physical stimulus or not, and not to the target designation of these events.

Response selection and initiation in speeded reactions: a pupillometric analysis.

Three studies are described in which the task-evoked pupillary response is recorded during simple and disjunctive reactions in order to examine its contribution as a measure of the motoric and cognitive aspects of performance in these tasks. In simple reactions a pupillary dilation began about 1.5 sec before the imperative stimulus and peaked about 1 sec after the stimulus. The rate of dilation was inversely related to the interstimulus interval. In disjunctive reactions, both "Go" and "No-Go" responses elicited significant dilations but the No-Go dilation was smaller than the Go dilation. When the response was delayed 2.5 sec after the discrimination stimulus, the dilation to both Go and No-Go responses was much reduced. The pupillary response related to response selection was estimated at 55% of that associated with motor preparation and execution. The probability of responding was found to affect the amplitude of the dilation to No-Go responses but not that to Go responses. The data point to a significant contribution of preparatory motor processing in No-Go reactions and to an overlap between decisional and motoric processing in disjunctive reactions.

Task-evoked pupillary responses, processing load, and the structure of processing resources.

A physiological measure of processing load or mental effort required to perform a cognitive task should accurately reflect within-task, between-task, and betweenindividual variations in processing demands. This article reviews all available experimental data and concludes that the task-evoked pupillary response fulfills these criteria. Alternative explanations are considered and rejected. Some implications for neurophysiological and cognitive theories of processing resources are discussed.

Task-evoked pupillary responses, processing load, and the structure of processing resources.

Task-evoked pupillary responses, processing load, and the structure of processing resources.