EEG variability: Task-driven or subject-driven signal of interest?

Neurons in the brain are seldom perfectly quiet. They continually receive input and generate output, resulting in highly variable patterns of ongoing activity. Yet the functional significance of this variability is not well understood. If brain signal variability is functionally relevant and serves as an important indicator of cognitive function, then it should be highly sensitive to the precise manner in which a cognitive system is engaged and/or relate strongly to differences in behavioral performance. To test this, we examined EEG activity in younger adults as they performed a cognitive skill learning task and during rest. Several measures of EEG variability and signal strength were calculated in overlapping time windows that spanned the trial interval. We performed a systematic examination of the factors that most strongly influenced the variability and strength of EEG activity. First, we examined the relative sensitivity of each measure to across-subject variation (within blocks) and across-block variation (within subjects). We found that the across-subject variation in EEG variability and signal strength was much stronger than the across-block variation. Second, we examined the sensitivity of each measure to different sources of across-block variation during skill acquisition. We found that key task-driven changes in EEG activity were best reflected in changes in the strength, rather than the variability, of EEG activity. Lastly, we examined across-subject variation in each measure and its relationship with behavior. We found that individual differences in response time measures were best reflected in individual differences in the variability, rather than the strength, of EEG activity. Importantly, we found that individual differences in EEG variability related strongly to stable indicators of subject identity rather than dynamic indicators of subject performance. We therefore suggest that EEG variability may provide a more sensitive subject-driven measure of individual differences than task-driven signal of interest.

Is looking older than one's actual age a sign of poor health?

BACKGROUND: Physicians often begin the physical examination with an assessment of whether a patient looks older than his or her actual age. This practice suggests an implicit assumption that patients who appear older than their actual age are more likely to be in poor health. OBJECTIVE: To determine the sensitivity and specificity of apparent age for the detection of poor health status. DESIGN: Cross-sectional. PATIENTS: A total of 126 outpatients (ages 30-70) from four primary care clinics and one general internal medicine clinic at an academic medical institution. MEASUREMENTS: With the patient's actual age provided, physicians (n = 58 internal medicine residents and general internal medicine faculty) viewed patient photographs and assessed how old each patient looked. For each physician, we examined the sensitivity and specificity of the difference between how old the patient looked and the patient's actual age for the detection of poor health, defined using SF-12 physical health and mental health scores. RESULTS: Using the threshold of looking ≥ 5 years older than actual age and with poor health defined as an SF-12 score ≥ 2.0 SD below age group norms, median sensitivity was 29% (IQR, 19% to 35%), median specificity 82% (IQR, 77% to 88%), median positive likelihood ratio 1.7 (IQR, 1.3 to 2.2), and median negative likelihood ratio 0.9 (IQR, 0.8 to 0.9). Using the threshold of looking ≥ 10 years older than actual age, median sensitivity was 5% (IQR, 2% to 9%) and median specificity was 99% (IQR, 96% to 100%). CONCLUSIONS: The diagnostic value of apparent age depends on how many years older than his or her actual age a patient looks. A physician's assessment that a patient looks ≥ 10 years older than his or her actual age has very high specificity for the detection of poor health.

The eyes know what you are thinking: eye movements as an objective measure of mind wandering.

Paralleling the recent work by Reichle, Reineberg, and Schooler (2010), we explore the use of eye movements as an objective measure of mind wandering while participants performed a reading task. Participants were placed in a self-classified probe-caught mind wandering paradigm while their eye movements were recorded. They were randomly probed every 2-3 min and were required to indicate whether their mind had been wandering. The results show that eye movements were generally less complex when participants reported mind wandering episodes, with both duration and frequency of within-word regressions, for example, becoming significantly reduced. This is consistent with the theoretical claim that the cognitive processes that normally influence eye movements to enhance semantic processing during reading exert less control during mind wandering episodes.

Turning the process-dissociation procedure inside-out: a new technique for understanding the relation between conscious and unconscious influences.

While there is now general agreement that memory gives rise to both conscious and unconscious influences, there remains disagreement concerning the process architecture underlying these distinct influences. Do they arise from independent underlying systems (e.g., Jacoby, 1991) or from systems that are interactive (e.g., Joordens & Merikle, 1993)? In the current paper we present a novel "inside-out" technique that can be used with the process-dissociation paradigm to arrive at more concrete conclusions concerning this central question and demonstrate this technique via a meta-analysis of currently published findings. Our results suggest that the data presented in these studies vary in ways most consistent with the assumption that conscious and unconscious influences behave independently.

Interhemispheric transfer of semantic information facilitates bilateral word recognition.

Language comprehension is left-lateralized but with variable contributions from the right hemisphere. When both hemispheres are stimulated simultaneously using divided visual field presentation, performance may be enhanced or hindered depending on the complexity of the task, and these effects may relate to independent processing in both hemispheres or to information transfer between hemispheres. Simultaneous stimulation of both hemispheres is thought to suppress interhemispheric interactions, but information transfer may nonetheless occur. Studies with simultaneous bilateral displays have demonstrated that semantic information from the contralateral visual field (and hemisphere) can facilitate relatedness judgments and lexical decisions. The current study extends this line of research by assessing semantic information transfer in a bilateral word identification task. Task manipulations involving directed spatial attention and asymmetric primes (e.g., ATOM → BOMB) were used to isolate automatic priming as opposed to top-down processing. The results revealed 2 main findings: (a) interhemispheric priming in the form of improved word recognition occurred specifically in conditions designed to isolate automatic transfer of semantic information, that is, in the attended visual field for the target word in asymmetric prime pairs, and (b) there is evidence for an asymmetrical transfer of semantic information, in that the subordinate left visual field-right hemisphere benefited more from such transfer. Together, these results demonstrate evidence for automatic interhemispheric transfer of semantic information, even under conditions of simultaneous bilateral display. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Utilizing virtual reality to improve the ecological validity of clinical neuropsychology: an FMRI case study elucidating the neural basis of planning by comparing the Tower of London with a three-dimensional navigation task.

Virtual reality (VR) was used to create an ecologically valid spatial-navigation task in hand with functional magnetic resonance imaging (fMRI) to articulate the neural basis of planning behavior. A virtual version of a traditional planning measure, the Tower of London, was also developed to ascertain convergent and divergent validity in terms of planning behavior and functional neuroanatomy. This VR-fMRI case study experiment was performed at 3.0 Tesla on a young healthy male subject. The obtained image data suggest both convergent and divergent specificity between the two conditions in terms of location and overall intensity of activation. Overall, the present case study provides supportive evidence that the activity of various brain regions associated with planning tasks is largely modulated by the ecological validity of the measure being used. This finding may extend to all domains of inquiry in neuropsychological research and assessment when deductive conclusions are formulated on the results of neuropsychological test measures that could be considered contrived in nature.

Modeling performance at the trial level within a diffusion framework: a simple yet powerful method for increasing efficiency via error detection and correction.

When faced with a relatively novel task, it is reasonable to assume that increases in performance efficiency depend upon processing adjustments that occur in response to errant or suboptimal performance. For such dynamic corrections to occur, the errors must first be noted, which can be challenging in contexts where no external feedback is provided. In the present article, the authors describe how a "double cross" error monitoring and correction process can be added to diffusion models of binary decision. The authors first outline the logick of our proposed error detection system, and then demonstrate that the addition of this double-cross process in the context of a simulation of lexical decision leads to more efficient responding. That is, with such a mechanism in place, the model was able to gradually respond more quickly and the distribution of errors became more consistent with human response patterns.

The mixed truth about frequency effects on free recall: effects of study list composition.

The mixed-list paradox is the finding that high-frequency words show a recall advantage in blocked lists, but that this advantage is reversed or nullified in mixed lists. We argue that this paradox has been poorly defined. Specifically, researchers should investigate random and alternating lists separately. We examine blocked, random, and alternating lists in our experiment. We hypothesize that a low-frequency recall advantage could arise due to asymmetrically strong links between low- and high-frequency words. Supporting our hypothesis, a low-frequency recall advantage is observed in the random list, as is an asymmetry of association. In the alternating list, no recall advantage is observed, and neither is any asymmetry of association. Our results offer a clear challenge to future research to (1) consider the associations between word frequencies and (2) consider random and alternating lists separately.

Intelligence as it relates to conscious and unconscious memory influences.

We examine the relationship between a measure of intelligence and estimates of conscious and unconscious memory influences derived using Jacoby's (Jacoby, L. L. [1991]. A process dissociation framework: Separating automatic from intentional uses of memory. Journal of Memory and Language, 30, 513-541.) process-dissociation procedure. We find a positive relationship between intelligence and conscious memory, and no relationship between intelligence and unconscious influences once the impact of conscious influences are removed (Experiment 1). We also find that when participants cannot engage in conscious strategies, such as when there is insufficient time for learning, the relationships observed in Experiment 1 are eliminated (Experiments 2A and 2B). Our results support the notion that individual differences in intelligence reflect differences in conscious strategic processes (Karis, D., Fabiani, M., & Donchin, E. [1984]. "P300" and memory: Individual differences in the von Restorff effect. Cognitive Psychology, 16, 177-216.) and not differences in mental speed (Eysenck, H. J. (1984). Intelligence versus behavior. The Behavioral and Brain Sciences, 7, 290-291; Jensen, A. R. [1982]. Bias in mental testing. New York, NY: Free Press).

Conducting research with non-clinical healthy undergraduates: does effort play a role in neuropsychological test performance?

Poor effort by examinees during neuropsychological testing has a profound effect on test performance. Although neuropsychological experiments often utilize healthy undergraduate students, the test-taking effort of this population has not been investigated previously. The purpose of the present study was to determine whether undergraduate students exercise variable effort in neuropsychological testing. During two testing sessions, participants (N = 36) were administered three Symptom Validity Tests (SVTs), the Test of Memory Malingering, the Dot Counting Test, and the Victoria Symptom Validity Test (VSVT), along with various neuropsychological tests. Analyses revealed 55.6% of participants in Session 1 and 30.8% of participants in Session 2 exerted poor effort on at least one SVT. Poor effort on the SVTs was significantly correlated with poor performance on various neuropsychological tests and there was support for the temporal stability of effort. These preliminary results suggest that the base rate of suboptimal effort in a healthy undergraduate population is quite high. Accordingly, effort may serve as a source of variance in neuropsychological research when using undergraduate students.

The similarities (and familiarities) of pseudowords and extremely high-frequency words: examining a familiarity-based explanation of the pseudoword effect.

The pseudoword effect is the finding that pseudowords (i.e., rare words or pronounceable nonwords) give rise to more hits and false alarms than words. Using the retrieving effectively from memory (REM) model of recognition memory, we tested a familiarity-based account of the pseudoword effect: Specifically, the pseudoword effect arises because pseudowords lack distinctive semantic meanings. Because semantics can differentiate orthographically similar words (e.g., horse vs. house), by lacking distinctive semantics, pseudowords have greater interitem similarity than words, and hence more familiarity, which gives rise to the pseudoword effect. Across two sets of simulations, we demonstrate that this account explains the pseudoword effect in addition to accounting for why the pseudoword effect is absent when irregular nonwords are compared with words. Furthermore, our modeling efforts suggest a novel experiment that leads us to the discovery of a new concordant effect. Namely, extremely high-frequency words behave like pseudowords (giving rise to more hits and false alarms than high-frequency words) and also have less distinctive semantics than high-frequency words. We conclude that our work provides strong evidence in favor of the familiarity-based accounts of the pseudoword effect. We discuss the implications of our research with regard to various issues surrounding the pseudoword effect and REM model.

Super Memory Bros.: going from mirror patterns to concordant patterns via similarity enhancements.

When memory is contrasted for stimuli belonging to distinct stimulus classes, one of two patterns is observed: a mirror pattern, in which one stimulus gives rise to higher hits but lower false alarms (e.g., the frequency-based mirror effect) or a concordant pattern, in which one stimulus class gives rise both to higher hits and to higher false alarms (e.g., the pseudoword effect). On the basis of the dual-process account proposed by Joordens and Hockley (2000), we predict that mirror patterns occur when one stimulus class is more familiar and less distinctive than another, whereas concordant patterns occur when one stimulus class is more familiar than another. We tested these assumptions within a video game paradigm using novel stimuli that allow manipulations in terms of distinctiveness and familiarity (via similarity). When more distinctive, less familiar items are contrasted with less distinctive, more familiar items, a mirror pattern is observed. Systematically enhancing the familiarity of stimuli transforms the mirror pattern to a concordant pattern as predicted. Although our stimuli differ considerably from those used in examinations of the frequency-based mirror effect and the pseudoword effect, the implications of our findings with respect to those phenomena are also discussed.

Selective attention versus selection for action: negative priming is not the result of distractors being unattended.

Using a novel referent size-selection task, MacDonald, Joordens, and Seergobin (1999; MacDonald & Joordens, 2000) found that negative priming persisted even when participants were encouraged to attend to distractors before selectively responding to targets. This finding suggested that negative priming is not caused by processes that operate on stimuli that are to be ignored in the traditional selective attention sense. Mackintosh, Mathews, and Holden's (2002) attempt to replicate the MacDonald et al. study resulted in the discovery of possible artifacts in the referent size-selection task, thereby making the implications with respect to the role of attention less clear. In the present study, we describe a different method for directing attention to distractors in a negative priming context, one that does not suffer from the same potential artifacts as the referent size-selection task. Our results are consistent with those found by MacDonald et al., in that negative priming persisted even when participants were explicitly encouraged to attend to distractors. Implications are discussed in the context of the related concepts of selective attention (e.g., Broadbent, 1965) versus selection for action (e.g., Allport, 1987).

Negate priming and multiple repetition: a reply to Grison and Strayer (2001).

Strayer and colleagues (Grison & Strayer, 2001; Malley & Strayer 1995; Strayer & Grison, 1999) have reported experiments in which negative priming by ignored stimuli occurred onlyfor stimuli that were repeatedly sampledfrom small sets. These results were argued to be inconsistent with episodic/mismatch accounts of negative priming. We show here that a dependence of negative priming on multiple repetition is wholly consistent with such theories. Furthermore, we argue that the inhibitory theory proposed by Strayer and colleagues cannot account for major findings regarding negative priming and that anomalies in the data reported by Grison and Strayer are more parsimoniously explained by episodic/mismatch accounts.

When timing the mind one should also mind the timing: biases in the measurement of voluntary actions.

Trevena and Miller (2002, this issue) provide further evidence that readiness potentials occur in the brain prior to the time that participants claim to have initiated a voluntary movement, a contention originally forwarded by Libet, Gleason, Wright, and Pearl (1983). In their examination of this issue, though, aspects of their data lead them to question whether their measurement of the initiation of a voluntary movement was accurate. The current article addresses this concern by providing a direct analysis of biases in this task. This was done by asking participants to make subjective timing decisions regarding a stimulus that could be measured objectively. Our findings suggest that their timing task was indeed biased such that participants' tend to report events as happening approximately 70 ms later than they actually happened. Implications for the original Libet et al. claims are discussed.

A clockwork orange: compensation opposing momentum in memory for location.

Libet, Gleason, Wright, and Pearl's (1983; Libet, 1985) influential work using a clock-watching task suggests that voluntary actions are initiated in motor cortex prior to the point where the participant claims to have initiated that action. Joordens, van Duijn, and Spalek (2002) showed that a bias exists in this task with respect to the participants' reports of initiation times. Joordens et al. assumed that this bias was primarily due to motion cues that are very much like those used to elicit phenomena such as representational momentum. In the present Experiment 1, it is demonstrated that this bias disappears when a mouse-click response is used in place of a temporal-order judgment. This finding, however, is actually more confusing than clarifying given that the procedural parallels with representational momentum are still present and should be supporting a bias. In the three subsequent experiments the view that a bias is indeed present, but that it is opposed by an opposite-acting compensation process, is proposed and tested. Implications for both representational momentum and for the general use of clock-watching tasks (e.g., Libet et al., 1983) are highlighted.