Response Time Distribution Analysis of Semantic and Response Interference in a Manual Response Stroop Task.

The Stroop interference effect—slower responses to the color of an incongruent color-word stimulus (e.g., GREEN in red ink) compared to a neutral stimulus (e.g., XXXX in red ink)—is one of the most robust findings in cognitive psychology. This thesis investigated why the effect is so robust, focusing on the unique perceptual architecture of the Stroop stimulus. Specifically, in a Stroop stimulus, the visual word form and color are integrated into a visual object, and hence attending to the color inevitably results in the word receiving attention as well. Across four empirical chapters, I demonstrated that presenting the distractor word in advance of a Stroop stimulus (a manipulation termed <i>distractor priming</i>—e.g., presenting the word GREEN in white ink followed by the same word GREEN in red ink) significantly reduced—and in some cases eliminated—the Stroop interference effect. I argued that this occurred because the distractor prime broke the integration of the visual word form and color in the Stroop stimulus, allowing rapid disengagement of attention from the word. Crucially, I examined response time (RT) distributions. In standard Stroop stimuli, the interference effect increased with slower responses, yielding a positively sloped delta plot. When the integration was disrupted by distractor priming, the delta slope flattened—that is, the interference effect remained constant across the RT distribution. Chapter 2 introduced the distractor priming paradigm. Consistent with prior studies of distractor priming that used oral color-naming responses, distractor priming in a manual Stroop task sped up responses to the color. Importantly, it eliminated the Stroop interference effect across the entire RT distribution (i.e., it removed the positively sloped delta). Chapter 3 demonstrated that this reduction in Stroop interference and removal of the positively sloped delta occurred only with a prime visually identical to the distractor. Stroop interference remained large, and the positively sloped delta persisted when the prime was conceptually related but not visually identical to the distractor word (e.g., LEAF - GREENred) or an auditory word (e.g., hearing “green”). Chapter 4 explored the relative “automaticity” of the distractor priming benefit and demonstrated that even when the word precue was only 50% predictive of the upcoming distractor word (unlike 100% as in the previous studies), Stroop interference was reduced and the positively sloped delta removed. Additionally, this experiment showed that the delta slope pattern of the Stroop interference effect found in the distractor-primed (identity precue) condition differed from that in the response-precue condition (e.g., the word RED followed by the word GREEN in red ink). Chapter 5 tested the assumption underlying the distractor priming benefit—that the positively sloped delta was removed when the integration between the word and color was disrupted—using the primed Stroop task. This paradigm differed from the standard Stroop task in that the word and color were not integrated into a single visual object; instead, the distractor word was presented ahead of a row of colored Xs. Across two experiments, RT distributions in the primed Stroop task mirrored those in distractor priming, in that Stroop interference was small and the positively sloped delta was eliminated. Together, these findings indicate that the robustness of the Stroop interference effect stems from the perceptual integration of the distractor word and color into a single visual object. Chapter 6 provides a discussion of the implication of our interpretation of Stroop interference on how the Stroop task is used as a tool to study selective attention.

Dissociable correlates of response conflict and error awareness in error-related brain activity

Object files play important roles in visual cognition, one of which is feature integration. However, their internal structure remains unknown. The current study investigated how multiple features of an object—color and shape—are integrated using a modified object-reviewing paradigm. In particular, we tested whether independent features or color-shape conjunction are bound to the file. A preview of two-colored objects was followed by a linking display. Then, a target was presented to judge whether the target contains any feature of the previews, regardless of their locations. Conditions in which both color and shape are matched with different corresponding preview locations were compared. If features are independently bound, facilitation in response time (RT) will increase additively as the number of location-shared features. If features are bundled, the RT facilitation occurs only when both features share the location. A series of experiments different in stimuli, the number of placeholders, and object motion showed different patterns of mean RT, but RT distribution analysis indicated that estimated nondecision time is consistent with the feature bundle hypothesis. The conjunction-based object preview benefit suggests that in object file formation, color and shape form a perceptual unit, and the unit is kept through object motion.

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Although response times (RTs) are the dependent measure of choice in the majority of studies of visual attention, changes in RTs can be hard to interpret. First, they are inherently ambiguous, since they may reflect a change in the central tendency or skew (or both) of a distribution. Second, RT measures may lack sensitivity, since meaningful changes in RT patterns may not be picked up if they reflect two or more processes having opposing influences on mean RTs. Here we describe RT distributions for repetition priming in visual search, fitting ex-Gaussian functions to RT distributions. We focus here on feature and conjunction search tasks, since priming effects in these tasks are often thought to reflect similar mechanisms. As expected, both tasks resulted in strong priming effects when target and distractor identities repeated, but a large difference between feature and conjunction search was also seen, in that the σ parameter (reflecting the standard deviation of the Gaussian component) was far more affected by search repetition in conjunction than in feature search. Although caution should clearly be used when particular parameter estimates are matched to specific functions or processes, our results suggest that analyses of RT distributions can inform theoretical accounts of priming in visual search tasks, in this case showing quite different repetition effects for the two differing search types, suggesting that priming in the two paradigms partly reflects different mechanisms.

The current study examined the effects of responses on error-adjacent trials (i.e., those immediately preceding or following errors) on age differences in measures of intraindividual variability and the shape of response time (RT) distributions on a two-back task. Removing error-adjacent responses reduced variability as measured by the coefficient of variation, but did so similarly for younger and older adults. However, older adults’ standard deviations (SDs) were less than those of younger adults with comparable RTs, raising questions regarding the validity of the coefficient of variation. An ex-Gaussian analysis revealed that removing the RTs on error-adjacent trials reduced the length of the tails of distributions and the skewness of the distributions. These properties were reduced more for older adults than for younger adults. These results indicate that the influence of error-adjacent trials should be considered when analyzing intraindividual variability and the shape of RT distributions to test theories of cognitive aging.

In response time (RT) research, RT outliers are typically excluded from statistical analysis to improve the signal-to-noise ratio. Nevertheless, there exist several methods for outlier exclusion. This poses the question, how these methods differ with respect to recovering the uncontaminated RT distribution. In the present simulation study, two RT distributions with a given population difference were simulated in each iteration. RTs were replaced by outliers following two different approaches. The first approach generated outliers at the tails of the distribution, the second one inserted outliers overlapping with the genuine RT distribution. We applied ten different outlier exclusion methods and tested, how many pairs of distributions significantly differed. Outlier exclusion methods were compared in terms of bias. Bias was defined as the deviation of the proportion of significant differences after outlier exclusion from the proportion of significant differences in the uncontaminated samples (before introducing outliers). Our results showed large differences in bias between the exclusion methods. Some methods showed a high rate of Type-I errors and should therefore clearly not be used. Overall, our results showed that applying an exclusion method based on z-scores / standard deviations introduced only small biases, while the absence of outlier exclusion showed the largest absolute bias.

Objective:To explore the usefulness of the Lowenstein-Acevedo Scales for Semantic Interference and Learning (LASSI-L) [Crocco et al, 2013], a novel memory-based cognitive stress test capitalizing on semantic interference, in Huntington’s Disease (HD).Participants and Methods:12 healthy adults (HA) and 14 individuals with manifest HD were administered the LASSI-L as part of an annual research visit with the UCSD Huntington’s Disease Clinical Research Center (HDCRC.) Participants in each group were well matched with regard to age and education. Individuals with manifest HD had an average MoCA score of 26, total functional capacity score of 10, and total motor score of 21 suggesting that they were in the early stages of HD. The LASSI-L examines different types of semantic interference that occur in the learning/encoding process. There are free and cued recall trials for two lists of semantically related words with certain trials specific to different aspects of semantic interference including proactive, retroactive, and failure to recover from proactive interference. T-tests for all recall trials and number of intrusions for each trial were conducted between HA and those with HD to examine whether HD renders one more prone to semantic interference in both encoding and retrieval memory processes.Results:Individuals with HD recalled fewer words on average than HA across all recall trials except for the initial free recall of the first word list. HD individuals recalled significantly fewer (∼1.5) words during the initial (t=-2.8, p=.005, Cohen’s d=2.7) and secondary (t=-2.9, p=.003, Cohen’s d=2.6) cued recall trials from the words on the first list. Individuals with HD also recalled significantly fewer words on initial free recall (t=-2.9, p=.003, Cohen’s d=2.6) and cued recall trials of the second list, with the initial cued recall (t=-2.8, p=.005, Cohen’s d=3.1) sensitive to proactive semantic interference and the second cued recall (t=-3.3, p=.001, Cohen’s d=2.6) sensitive to failure to recover from proactive semantic interference. In addition, individuals with HD also recalled significantly fewer (∼2.2) words on delayed cued recall of the first list, a measure of retroactive semantic interference, than HA (t=-4.8, p&lt;.001, Cohen’s d=2.4). Lastly, individuals with HD recalled fewer (∼4.1) words than HA on delayed free recall of both word lists (t=-3.5, p&lt;.001, Cohen’s d=5.9). The groups did not differ significantly with regard to number of total intrusions per trial.Conclusions:Overall, our study supports the usefulness of the LASSI-L for neuropsychological assessment of HD in clinical and research settings. In comparison to a demographically similar group of HA, individuals with manifest HD showed significant differences in frontally mediated retrieval processes as well as semantic interference processes that affect efficient encoding of novel information.

A behavioral and eye movement study on inhibitory processing of action memory

The study investigated the consequences of age-related decline in inhibition processes on intentional switching between bimanual coordination patterns. Fifteen young (24±2.8 years) and 20 older adults (69±5.3 years) performed Stroop tasks and bimanual coordination tasks. Stroop tasks included neutral, congruent, and incongruent conditions. Response time and error rate were measured. Bimanual coordination tasks consisted of performing in-phase (IP) and anti-phase (AP) patterns. Participants were requested to switch as quickly as possible from one pattern to the other, resulting in two different switching directions (AP to IP; IP to AP). Mean and standard deviation (SD) of the continuous relative phase (CRP) were calculated pre- and post-switching for each participant. Total switching time (TST) was measured. The switching phase was also decomposed into reaction time (RT) and reversal time (REvT). Pearson correlation analyses were performed to test for correlations between: (i) SD of CRP and response time in Stroop tasks, and (ii) switching times (TST, RT, RevT) and response time in Stroop task, respectively. In addition, parallel mediation analyses were conducted. Results showed that: (i) the AP pattern was less stable than the IP pattern in both young and older adults, (ii) coordination patterns were less stable in older adults, (iii) response times in Stroop task were longer in the incongruent condition, and (iv) RespTs were longer in older than in young participants, whatever the condition. In the bimanual coordination task, RT, RevT, and TST increased with age. The stability of the IP pattern was correlated with the response times observed in neutral and congruent conditions, while the stability of the AP pattern was correlated with response time observed in the incongruent condition. Correlation and mediation analyses showed that, in the AP to IP switching direction, RT and RevT were both significantly correlated with response times observed in the incongruent condition of Stroop task. These findings suggest that inhibition processes are involved in switching between bimanual coordination patterns, at least to trigger the early phase of switching. They also support the hypothesis that inhibition processes are more involved in maintaining the AP pattern and switching to the IP pattern. Finally, age-related changes in switching times seem to be prominently mediated by alterations of inhibition processes.

Motor conflict in Stroop tasks: Direct evidence from single-trial electro-myography and electro-encephalography

P.3.c.025 Change of cognitive functions in switching of risperidone for chronic schizophrenic patients

Psychological data, particularly measurements obtained sequentially in experiments designed to test theories of human cognition, are often treated as independent and identically distributed samples from a single distribution that describes the cognitive process. This assumption is made for mathematical and analytic convenience; it is widely appreciated that such data are in fact mixtures from two or more processes, only a subset of which are associated with the cognitive process of interest. Our modeling framework describes response times (RTs) as arising from a mixture of three distinct distributions. Transitions across the distributions are governed by a hidden Markov structure whose states produce either fast, average, or slow RTs. This process is nested within a second hidden Markov structure, producing an “environment” process that allows the distribution of the response modes to evolve due to both internal factors (such as fatigue and distractions) and external factors (such as changing task demands). We performed a detection experiment designed to elicit responses under three environments that mimic external conditions that influence latent response modes. We present our hierarchical model and demonstrate its fit on the experimental data. We also demonstrate the model’s fit in the case when external conditions were not manipulated as part of the experimental process.

In this work, a preliminary conceptual model of the hydrogeological functioning of a binary karst aquifer located in southern Spain is presented, based on the natural responses of the springs and the dye tracer tests. Results derived from the long-term analysis of cross-correlation function (CCF) (global average time of recharge input) have been validated with those obtained from a dye tracer test, performed during a specific recharge event. The overall response times (CCF results) obtained for the three springs studied were 58 (SP-1), 72 (SP-3), and 81 h (SP-2). This pattern in response times was contrasted with the first detection times of the BTC-Tracer Breakthrough Curve—at the same three springs (30.9, 35.3, and 47 h) and their respective recovery rates (2.03, 21.9, and 78.4% for S1, S2, and S3, respectively). The distribution of response times, both those determined by long-term statistical analysis and the ones derived from the use of dye tracer test, is directly related to the karst network development in each of the drainage routes. Additionally, the rate of tracer recovery at each of the springs is linked to the hierarchy of flow paths from the selected injection point toward each spring, within the overall drainage network scheme. An accurate knowledge of all factors affecting the hydrogeological behavior as well as groundwater flow paths (from swallow holes to the springs) is crucial for suitable management of the resource and to mitigate the pollution risks derived from fast infiltration of surface water.KeywordsCross-correlationDye tracer testKarst aquiferTime lagAquifer functioning

A transaction scheduling mechanism is designed for a shared memory, multiprocessor database system. The scheduler used is a variant of static locking, adapted for real time and more than one processor. It is assumed that transactions arrive according to a Poisson process, execution times of transactions are independent and exponentially distributed and all transactions use the same number of data items. The system is then represented as a Markov model. A steady state is derived from this model. By examining the path through the system of a single transaction, a recursive relation that describes all moments of a transaction's response time is derived. The response time distribution is approximated by fitting a distribution to the first two moments. Simulation shows that this approximation gives excellent results.