The Viability of Cooperation Based on Interpersonal Commitment

A prominent explanation of cooperation in repeated exchange is reciprocity (e.g. Axelrod, 1984). However, empirical studies indicate that exchange partners are often much less intent on keeping the books balanced than Axelrod suggested. In particular, there is evidence for commitment behavior, indicating that people tend to build long-term cooperative relationships characterised by largely unconditional cooperation, and are inclined to hold on to them even when this appears to contradict self-interest. Using an agent-based computational model, we examine whether in a competitive environment commitment can be a more successful strategy than reciprocity. We move beyond previous computational models by proposing a method that allows to systematically explore an infinite space of possible exchange strategies. We use this method to carry out two sets of simulation experiments designed to assess the viability of commitment against a large set of potential competitors. In the first experiment, we find that although unconditional cooperation makes strategies vulnerable to exploitation, a strategy of commitment benefits more from being more unconditionally cooperative. The second experiment shows that tolerance improves the performance of reciprocity strategies but does not make them more successful than commitment. To explicate the underlying mechanism, we also study the spontaneous formation of exchange network structures in the simulated populations. It turns out that commitment strategies benefit from efficient networking: they spontaneously create a structure of exchange relations that ensures efficient division of labor. The problem with stricter reciprocity strategies is that they tend to spread interaction requests randomly across the population, to keep relations in balance. During times of great scarcity of exchange partners this structure is inefficient because it generates overlapping personal networks so that often too many people try to interact with the same partner at the same time.Interpersonal Commitment, Fairness, Reciprocity, Agent-Based Simulation, Help Exchange, Evolution

The characteristics of cognitive neuroscience tests in a schizophrenia cognition clinical trial: Psychometric properties and correlations with standard measures.

In comparison to batteries of standard neuropsychological tests, cognitive neuroscience tests may offer a more specific assessment of discrete neurobiological processes that may be aberrant in schizophrenia. However, more information regarding psychometric properties and correlations with standard neuropsychological tests and functional measures is warranted to establish their validity as treatment outcome measures. The N-back and AX-Continuous Performance Task (AX-CPT) are two promising cognitive neuroscience tests designed to measure specific components of working memory and contextual processing respectively. In the current study, we report the psychometric properties of multiple outcome measures from these two tests as well as their correlations with standard neuropsychological measures and functional capacity measures. The results suggest that while the AX-CPT and N-back display favorable psychometric properties, they do not exhibit greater sensitivity or specificity with functional measures than standard neurocognitive tests

Improving Memory Through N-back Training

Jaeggi and colleagues have claimed that fluid intelligence may be improved through a cognitive training regime utilising the n-back task; maintaining that the improvement in Gf is realised through melioration in working memory (WM). To date there has been no evidence to support this assertion, however Jaeggi, Buschkuehl, Jonides, and Perrig (2008) obtained a significant improvement in short term memory (STM). The current study examined the near transfer mechanisms of the single n-back task; specifically STM and WM as operationalised through the Woodcock-Johnson III Tests of Cognitive Abilities. Forty-seven participants were divided into experimental (n = 26) and active control groups (n = 21); and engaged in 20-daily, 20-minute training sessions over a 30-day period using either a single n-back, or a combined verbal and general knowledge task respectively. Before and after the training process STM and WM psychometric tests were administered, and subsequently compared for performance improvements. The constructs of WM and STM were found not to be significantly improved by single n-back training. Furthermore, pre-training test scores, and test gain scores were found to be independent of age

Improving memory using N-back training

Investigations into n-back training and near transfer to short-term memory (STM) and working memory (WM) have realised inconsistent results. A significant transfer to STM was reported using dual n-back training (Jaeggi, Buschkuehl, Jonides, & Perrig, 2008). However, the majority of studies have found no significant transfer to WM as operationalised by complex span tasks using either single or dual n-back training. The current study examined the single n-back task and near transfer to STM and WM as operationalised by the Woodcock-Johnson III Tests of Cognitive Abilities (Mather & Woodcock-Johnson, 2001). Forty-seven participants were divided into experimental treatment (n = 26) and active control (n = 21) groups; and engaged in 20 daily, 20-minute training sessions over a 30-day period using either a single n-back task, or a combination of two general knowledge tasks respectively. STM and WM psychometric tests were administered before and after the 30-day training process. No significant difference was found between pre- and post-training STM or WM scores, indicating both constructs were unlikely near transfer mechanisms for single nback training. There was concern that the non-significant WM finding may have been confounded as there is evidence to suggest that the single n-back task and one of the active control group tasks both relied on recognition for resolution. The small effect size associated with single n-back transfer to STM implied that this outcome was independent of the active control group. Furthermore, the non-significant result for STM suggests that single and dual n-back tasks differ in their transfer properties

Improved Working Memory but No Effect on Striatal Vesicular Monoamine Transporter Type 2 after Omega-3 Polyunsaturated Fatty Acid Supplementation

Studies in rodents indicate that diets deficient in omega-3 polyunsaturated fatty acids (n-3 PUFA) lower dopamine neurotransmission as measured by striatal vesicular monoamine transporter type 2 (VMAT2) density and amphetamine-induced dopamine release. This suggests that dietary supplementation with fish oil might increase VMAT2 availability, enhance dopamine storage and release, and improve dopamine-dependent cognitive functions such as working memory. To investigate this mechanism in humans, positron emission tomography (PET) was used to measure VMAT2 availability pre- and post-supplementation of n-3 PUFA in healthy individuals. Healthy young adult subjects were scanned with PET using [11C]-(+)-α-dihydrotetrabenzine (DTBZ) before and after six months of n-3 PUFA supplementation (Lovaza, 2 g/day containing docosahexaenonic acid, DHA 750 mg/d and eicosapentaenoic acid, EPA 930 mg/d). In addition, subjects underwent a working memory task (n-back) and red blood cell membrane (RBC) fatty acid composition analysis pre- and post-supplementation. RBC analysis showed a significant increase in both DHA and EPA post-supplementation. In contrast, no significant change in [11C]DTBZ binding potential (BPND) in striatum and its subdivisions were observed after supplementation with n-3 PUFA. No correlation was evident between n-3 PUFA induced change in RBC DHA or EPA levels and change in [11C]DTBZ BPND in striatal subdivisions. However, pre-supplementation RBC DHA levels was predictive of baseline performance (i.e., adjusted hit rate, AHR on 3-back) on the n-back task (y = 0.19+0.07, r2 = 0.55, p = 0.009). In addition, subjects AHR performance improved on 3-back post-supplementation (pre 0.65±0.27, post 0.80±0.15, p = 0.04). The correlation between n-back performance, and DHA levels are consistent with reports in which higher DHA levels is related to improved cognitive performance. However, the lack of change in [11C]DBTZ BPND indicates that striatal VMAT2 regulation is not the mechanism of action by which n-3 PUFA improves cognitive performance. © 2012 Narendran et al

Visual Memory Improvement in Recognition

Fluid intelligence and working memory might be improved by training on a visual working memory n-back task (Jaeggi, Buschkuehl, Jonides & Perrig, 2008). Previous honours projects at ECU have shown no improvement in fluid intelligence due to n-back training, and a significant increase in fluid intelligence associated with general knowledge and vocabulary task training. One possibility may be that visual recognition memory may mediate the improvement in fluid intelligence (Jaeggi et al., 2008). The present study therefore investigates whether n-back training can increase visual recognition memory. A sample of 47 participants underwent 20 days of cognitive training on either the single n-back task (n = 26) or a combined general knowledge and vocabulary task (n =21). Results showed that training using the single n-back task did not significantly increase visual recognition memory scores when compared with general knowledge and vocabulary training. However, participants who had high scores on the vocabulary training task did improve their visual recognition scores significantly more than participants who had low scores. During debrief, participants in the high scoring vocabulary training group said that they used shape recognition strategies to improve their performance. It is suggested that the vocabulary task may be better at training visual recognition than the n-back task and therefore fluid intelligence

Visual memory improvement in recognition

Fluid intelligence and working memory has been improved by training on a visual working memory n-back task (Jaeggi, Buschkuehl, Jonides & Perrig, 2008). The present study investigated whether n-back training can improve visual memory using a test of visual recognition. A sample of 47 participants were trained for 20 days on either the single n-back task (n = 26) or a general knowledge and vocabulary task (n = 21). The results showed that training using the single n-back task did not significantly increase scores on a test of visual recognition when compared with general knowledge and vocabulary training. However, when initial scores were compared with final scores at completion of the training period, participants who had a high gain in scores on the vocabulary training task improved their visual recognition scores significantly more than those participants who had a low gain in scores on the vocabulary training task. This pattern was not repeated for those participants who were trained in the n-back task. During debrief, participants in the high gain vocabulary training group described shape recognition strategies which they used to improve their performance. It was concluded that the vocabulary task was more successful at training visual recognition than the n-back task which suggested the vocabulary task had a confounding effect on the results of this experiment

Working Memory, Attention Control, and the N-Back Task: A Question of Construct Validity

The n-back task requires participants to decide whether each stimulus in a sequence matches the one that appeared n items ago. Although n-back has become a standard ?executive? working memory (WM) measure in cognitive neuroscience, it has been subjected to few behavioral tests of construct validity. A combined experimental–correlational study tested the attention-control demands of verbal 2- and 3-back tasks by presenting n — 1 ?lure? foils. Lures elicited more false alarms than control foils in both 2- and 3-back tasks, and lures caused more misses to targets that immediately followed them compared with control targets, but only in 3-back tasks. N-back thus challenges control over familiarity-based responding. Participants also completed a verbal WM span task (operation span task) and a marker test of general fluid intelligence (Gf; Ravens Advanced Progressive Matrices Test; J. C. Raven, J. E. Raven, & J. H. Court, 1998). N-back and WM span correlated weakly, suggesting they do not reflect primarily a single construct; moreover, both accounted for independent variance in Gf. N-back has face validity as a WM task, but it does not demonstrate convergent validity with at least 1 established WM measure

Blur detection is unaffected by cognitive load

Blur detection is affected by retinal eccentricity, but is it also affected by attentional resources? Research showing effects of selective attention on acuity and contrast sensitivity suggests that allocating attention should increase blur detection. However, research showing that blur affects selection of saccade targets suggests that blur detection may be pre-attentive. To investigate this question, we carried out experiments in which viewers detected blur in real-world scenes under varying levels of cognitive load manipulated by the N-back task. We used adaptive threshold estimation to measure blur detection thresholds at 0°, 3°, 6°, and 9° eccentricity. Participants carried out blur detection as a single task, a single task with to-be-ignored letters, or an N-back task with four levels of cognitive load (0, 1, 2, or 3-back). In Experiment 1, blur was presented gaze-contingently for occasional single eye fixations while participants viewed scenes in preparation for an easy picture recognition memory task, and the N-back stimuli were presented auditorily. The results for three participants showed a large effect of retinal eccentricity on blur thresholds, significant effects of N-back level on N-back performance, scene recognition memory, and gaze dispersion, but no effect of N-back level on blur thresholds. In Experiment 2, we replicated Experiment 1 but presented the images tachistoscopically for 200 ms (half with, half without blur), to determine whether gaze-contingent blur presentation in Experiment 1 had produced attentional capture by blur onset during a fixation, thus eliminating any effect of cognitive load on blur detection. The results with three new participants replicated those of Experiment 1, indicating that the use of gaze-contingent blur presentation could not explain the lack of effect of cognitive load on blur detection. Thus, apparently blur detection in real-world scene images is unaffected by attentional resources, as manipulated by the cognitive load produced by the N-back task