Determinants of pigeons' choices in token-based self-control procedures

Four pigeons were exposed to a token-based self-control procedure with stimulus lights serving as token reinforcers. Smaller-reinforcer choices produced one token immediately; larger-reinforcer choices produced three tokens following a delay. Each token could be exchanged for 2-s access to food during a signaled exchange period each trial. The main variables of interest were the exchange delays (delays from the choice to the exchange stimulus) and the food delays (also timed from the choice), which were varied separately and together across blocks of sessions. When exchange delays and food delays were shorter following smaller-reinforcer choices, strong preference for the smaller reinforcer was observed. When exchange delays and food delays were equal for both options, strong preference for the larger reinforcer was observed. When food delays were equal for both options but exchange delays were shorter for smaller-reinforcer choices, preference for the larger reinforcer generally was less extreme than under conditions in which both exchange and food delays were equal. When exchange delays were equal for both options but food delays were shorter for smaller-reinforcer choices, preference for the smaller reinforcer generally was less extreme than under conditions in which both exchange and food delays favored smaller-reinforcer choices. On the whole, the results were consistent with prior research on token-based self-control procedures in showing that choices are governed by reinforcer immediacy when exchange and food delays are unequal and by reinforcer amount when exchange and food delays are equal. Further, by decoupling the exchange delays from food delays, the results tentatively support a role for the exchange stimulus as a conditioned reinforcer.     

Completing visual contours: The relationship between relatability and minimizing inflections

Visual completion is a ubiquitous phenomenon: Human vision often constructs contours and surfaces in regions that have no sharp gradients in any image property. When does human vision interpolate a contour between a given pair of luminance-defined edges? Two different answers have been proposed: relatability and minimizing inflections. We state and prove a proposition that links these two proposals by showing that, under appropriate conditions, relatability is mathematically equivalent to the existence of a smooth curve with no inflection points that interpolates between the two edges. The proposition thus provides a set of necessary and sufficient conditions for two edges to be relatable. On the basis of these conditions, we suggest a way to extend the definition of relatability (1) to include the role of genericity, and (2) to extend the current all-or-none character of relatability to a graded measure that can track the gradedness in psychophysical data.     

FUNCTIONAL MAGNETIC RESONANCE IMAGING OF SEMANTIC MEMORY PROCESSES IN THE FRONTAL LOBES

Abstract— Frontal-lobe activation during semantic memory performance was examined using functional magnetic resonance imaging (fMRI), a noninvasive technique for localizing neural activity associated with cognitive function. Left inferior prefrontal cortex was more activated for semantic than for perceptual encoding of words, and for initial than for repeated semantic encoding of words. Decreased activation for semantic encoding of repeated words reflects repetition priming, that is, implicit retrieval of memory gained in the initial semantic encoding of a word. The left inferior prefrontal region may sub-serve semantic working memory processes that participate in semantic encoding and that have decreased demands when such encoding can be facilitated by recent semantic experience. These results demonstrate that fMRI can visualize changes in an individual's brain function associated with the encoding and retrieval of new memories.     

Vacancy-mediated structural changes in Au–Cu nanoparticles

We report the formation of new phases in bimetallic Au–Cu nanoparticles. These phases were observed in nanoparticle synthesised by adopting a three-step protocol in a single pot. Nanoparticles at 180°C for 1?h led to the formation of single-phase solid solution of Cu in Au. Subsequent heat treatment at 290°C for 2?h of these Au–Cu nanoparticles revealed three new phases. One of them relates to the modification of occupancy of Cu in an ordered AuCu tetragonal phase (tP4). This cell although retains tetragonal symmetry but displays metrical properties akin to that of a cube. The other two relates to vacancy ordering along <111> directions in the {111} planes of an ordered AuCu3 cubic phase (cP4). On the one hand, statistical occupancy of vacancy on Cu site in this cell leads to the reduction of cell size from ～3.75?Å to ～3.5?Å whereas ordering of vacant layer on the other hand gives rise to symmetry breaking. Former continues to display cubic symmetry whereas latter transforms to a trigonal cell.     

The Role of Patient Religiosity in the Evaluation and Treatment Outcomes for Chronic HCV Infection

To determine the influence of patient religiosity on the outcome of treatment of hepatitis C infection, a prospective, blinded, cohort study was performed on hepatitis C-infected patients categorized as ‘higher religiosity’ and ‘lower religiosity’ based on responses to a religiosity questionnaire. Comparisons were made between high and low religiosity patients on demographics, pre-treatment laboratory values, and response to treatment. Eighty-seven patients with complete questionnaires were placed in either higher (38) or lower (49) religiosity cohort. The patients (60% female) were ethnically diverse: African-American 39%; Hispanic 31%; white 29%. African-American race (P = 0.001) and female gender (P = 0.026) were associated with higher religiosity. The frequency of being offered treatment, accepting treatment, and completing treatment was similar in both religiosity cohorts (P = 0.234, 0.809, 0.367). Fifty-six patients completed the 24- or 48-week treatment with peginterferon and ribavirin. Depression was more frequent in the low religiosity group (38.2% vs. 4.6%, P = 0.005). Sustained viral response rate at 3–6-month post-therapy was similar in the higher (50%) and lower (57.6%) religiosity cohorts (P = 0.580; n = 55). Logistic regression modeling revealed that males having higher religiosity gave greater odds of SVR than those with lower religiosity (OR 21.3; 95% CI 1.1–403.9). The level of religiosity did not affect the decision to begin treatment for chronic HCV infection and was not associated with a better treatment outcome. A higher level of religiosity was associated with less depression among patients.     

Strength of default mode resting-state connectivity relates to white matter integrity in children

A default mode network of brain regions is known to demonstrate coordinated activity during the resting state. While the default mode network is well characterized in adults, few investigations have focused upon its development. We scanned 9-13-year-old children with diffusion tensor imaging and resting-state functional magnetic resonance imaging. We identified resting-state networks using Independent Component Analysis and tested whether the functional connectivity between the medial prefrontal cortex (mPFC) and posterior cingulate cortex (PCC) depends upon the maturation of the underlying cingulum white matter tract. To determine the generalizability of this relationship, we also tested whether functional connectivity depends on white matter maturity between bilateral lateral prefrontal cortex (lateral PFC) within the executive control network. We found a positive relationship between mPFC-PCC connectivity and fractional anisotropy of the cingulum bundle; this positive relationship was moderated by the age of the subjects such that it was stronger in older children. By contrast, no such structure-function relationship emerged between right and left lateral PFC. However, functional and structural connectivity of this tract related positively with cognitive speed, fluency, and set-switching neuropsychological measures.     

Application of pharmacological fMRI to developmental psychiatric disorders

Functional magnetic resonance imaging of neural activity induced by pharmacological stimulation (phMRI) is a promising technique for revealing pathophysiology and etiology of developmental psychiatric disorders. Recent investigations of the dopaminergic system have made possible the use of phMRI as a non‐invasive assay for neurotransmitter function. This paper explores applications of phMRI for identification of neurophysiological trait‐dependent and clinical state‐dependent mechanisms that can define biologically valid diagnostic criteria for developmental psychiatric disorders. Further, applications of phMRI for investigations of neurochemical changes induced by long‐term drug exposure, alternative therapies and normal brain maturation are discussed. The paper ends by highlighting methodological challenges posed by experimental control of pharmacological stimulation that is essential for valid interpretation of phMRI results.