Jan Lammertyn

Parietal Representation of Symbolic and Nonsymbolic Magnitude

The close behavioral parallels between the processing of quantitative information conveyed by symbolic and non-symbolic stimuli led to the hypothesis that there exists a common cerebral representation of quantity (Dehaene, Dehaene-Lambertz, & Cohen, 1998). The neural basis underlying the encoding of number magnitude has been localized to regions in and around the intraparietal sulcus (IPS) by brain-imaging studies. However, it has never been demonstrated that these same regions are also involved in the quantitative processing of nonsymbolic stimuli. Using functional brain imaging, we explicitly tested the hypothesis of a common substrate. Angles, lines, and two-digit numbers were presented pairwise, one to the left and one to the right of the fixation point. In the three comparison tasks, participants (n = 18) pressed the key on the side of the largest quantity. In the three control tasks, they indicated the side on which dimming occurred. A conjunction analysis between the three subtractions (comparison task-control task) revealed a site in left IPS that is specifically responsive when two stimuli have to be compared quantitatively, irrespective of stimulus format. The results confirm the hypothesis that quantity is represented by a common mechanism for both symbolic and nonsymbolic stimuli in IPS. In addition, the interaction between task and type of stimulus identified a region anterior to the conjunction site, not specific for quantitative processing, but reflecting general processes loaded by number processing.

Irrelevant digits affect feature-based attention depending on the overlap of neural circuits

Feature-based attention was investigated by examining the effect of irrelevant information on the processing of relevant information. In all experiments, irrelevant information consisted of digits whose semantic information is known to be processed in parietal areas. Between experiments we varied the degree of parietal involvement in the processing of the relevant feature. The influence of the irrelevant digit on the binary manual response task on the relevant feature was measured by the SNARC effect, a spatial numerical association of response codes demonstrating faster left than right hand responses for small numbers and faster right than left hand responses for large numbers. When processing of the relevant feature depended on parietal cortex, as is the case for orientation processing (exps. 1 and 4), there was an effect of the digits semantic value on response times. Conversely, there was no effect of the irrelevant digit on the processing of color (exps. 2 and 3) or shape (exp. 5), which rely only minimally on parietal resources. After ruling out alternative explanations we conclude that the efficiency of feature-based attention is determined by the degree of neural overlap of structures dedicated to process relevant and irrelevant information.

Tscope: A C library for programming cognitive experiments on the MS windows platform.

Tscope is a C/C11 programming library designed for programming experiments that run on Windows 2000/XP. It is intended for a public of experimental psychologists with moderate programming skills, who are accustomed to writing their own experimental programs for DOS but have not made the step to Windows-based programming yet. It provides molecular functions for graphics, sound, timing, randomization, and response registration. Together with ANSI-C standard library functions and the powerful C syntax, this set of functions gives the experimenter the opportunity to program virtually any experiment one can come up with. Tscope is completely based on free software, is distributed under the GNU General Public License, and is available at expsy.ugent.be/tscope. An integrated development environment for compiling and running Tscope programs is also freely available.

Processing of Abstract Ordinal Knowledge in the Horizontal Segment of the Intraparietal Sulcus

The anterior intraparietal sulcus, and more specifically its horizontal segment (hIPS), is known to play a crucial role in the cognitive representation of numerical quantity. Whether the involvement of hIPS is restricted to the processing of numerical information or generalizes to non-numerical ordinal dimensions remains an open question. Using functional magnetic resonance imaging during comparison tasks, we demonstrate that the hIPS is equally responsive to numbers and letters, indicating that hIPS is also involved in the representation and processing of non-numerical ordinal series. This extends the numerical processing function of IPS into the realm of abstract knowledge processing.

How is reward sensitivity related to bodyweight in children

Previous research assumes that there are two seemingly opposing hypotheses for the relation between reward sensitivity (RS) and bodyweight: hyper-responsiveness model and Reward Deficiency Syndrome (RDS), leading to the proposition of a feed forward process of weight gain. High RS may contribute to overeating and weight-gain among normal weight individuals. Over time the excessive food-intake may evolve in a down-regulation of dopamine (RDS), resulting in overeating as a form of self-medication and the progression to obesity. This process was evidenced in adults showing a curvi-linear relationship between self-reported RS and BMI. The aim of the current study was to investigate the association between self-reported RS and BMI in children (10-15 years). The results confirm the non-linear relationship between RS and bodyweight and support the suggestion of the same feed forward process in children. These findings imply that it is crucial to reduce the intake of high palatable foods in high RS children to prevent the decrease in RS and reduce the risk for future weight gain.

Semantic Influences on Feature-Based Attention Due to Overlap of Neural Circuits

SEMANTIC INFLUENCES ON FEATURE-BASED ATTENTION DUE TO OVERLAP OF NEURAL CIRCUITS Jan Lammertyn1, Wim Fias1 and Johan Lauwereyns2 (1Department of Experimental Psychology, Ghent University, Belgium and 2Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, Bethesda, Maryland, USA)

Identifying students with dyslexia in higher education

An increasing number of students with dyslexia enter higher education. As a result, there is a growing need for standardized diagnosis. Previous research has suggested that a small number of tests may suffice to reliably assess students with dyslexia, but these studies were based on post hoc discriminant analysis, which tends to overestimate the percentage of systematic variance, and were limited to the English language (and the Anglo-Saxon education system). Therefore, we repeated the research in a non-English language (Dutch) and we selected variables on the basis of a prediction analysis. The results of our study confirm that it is not necessary to administer a wide range of tests to diagnose dyslexia in (young) adults. Three tests sufficed: word reading, word spelling and phonological awareness, in line with the proposal that higher education students with dyslexia continue to have specific problems with reading and writing. We also show that a traditional postdiction analysis selects more variables of importance than the prediction analysis. However, these extra variables explain study-specific variance and do not result in more predictive power of the model.

Exploratory Study on Domain-Specific Determinants of Opiate-Dependent Individuals’ Quality of Life

Background/Aims: Studies on determinants of quality of life (QoL) among opiate-dependent individuals are scarce. Moreover, findings concerning the role of severity of drug use are inconsistent. This exploratory study investigates the association between domain-specific QoL and demographic, social, person, health and drug-related variables, and potential indirect effects of current heroin use on opiate-dependent individuals’ QoL. Methods: A cohort of opiate-dependent individuals who started outpatient methadone treatment at least 5 years previously (n = 159) were interviewed about their current QoL, psychological distress, satisfaction with methadone treatment and the severity of drug-related problems using the Lancashire Quality of Life Profile, the Brief Symptom Inventory, the Verona Service Satisfaction Scale for Methadone Treatment and the EuropASI. Results: None of the QoL domains were defined by the same compilation of determinants. No direct effect of current heroin use on QoL was retained, but path analyses demonstrated its indirect effects on the domains of ‘living situation’, ‘finances’ and ‘leisure and social participation’. Conclusion: These findings illustrate the particularity of each QoL domain and the need for a multidimensional approach to the concept. The relationship between current heroin use and various domains of opiate-dependent individuals’ QoL is complex, indirect and mediated by psychosocial and treatment-related variables.

Negative priming with numbers: No evidence for a semantic locus

Selective attention has been studied extensively using the negative priming (NP) paradigm. An important issue regards the representational level at which NP occurs. We investigated this issue by using numbers as stimuli. Because numbers have a well-defined semantic organization, which can be clearly measured by means of the distance effect, they are very suitable for testing the assumption that NP is situated at a central semantic level. Four experiments are presented in which the numerical distance between prime distractor and probe target was manipulated. The task was magnitude comparison. Target and distractor were defined on the basis of colour. In Experiment 1, all numbers were presented in Arabic format; NP was observed only with identical prime distractor and probe target, and no distance-related NP was observed. This could not be explained by a decay of inhibition since in Experiment 2 similar results were obtained with a shortened response-to-stimulus interval. Experiment 3 showed that these observations also hold for numbers presented verbally. Nevertheless, a cross-notational experiment with Arabic prime and verbal probe (Experiment 4) revealed no NP whatsoever and excluded the possibility that the absence of distance-related negative priming was the result of a fine-tuned inhibitory mechanism operating at the semantic level. The results are considered in the light of current theories of negative priming.

Illicit Drug Use in the Flemish Nightlife Scene between 2003 and 2009

Aims: Given the importance of party people as innovators and early adaptors in the diffusion of substance use, and given the lack of longitudinal scope in studies of the nightlife scene, we explored changes in illicit drug use among young people participating in the nightlife scene in Flanders. Methods: A survey among party people selected at dance events, rock festivals and clubs was held in the summer of 2003 and repeated in 2005, 2007 and 2009. In total, 2,812 respondents filled in a questionnaire on the use of cannabis, ecstasy, cocaine, amphetamines, GHB and ketamine. Results: The results of the multiple logistic regression analyses show that in the group of frequent pub visitors, the predicting probability of cannabis use increased over time, while the gap in drug use between dance music lovers and non-lovers of dance music narrowed. For cocaine use during the last year, an increase was found related to the housing situation (alone or with parents) of respondents. While the odds of using ecstasy decreased over the years, the odds of using GHB increased. Conclusion: We can conclude that monitoring emerging trends, which can be quickly observed in the nightlife scene, provides meaningful information for anticipating possible trends.