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.     

Choral reading with filtered speech: effect on stuttering

This study investigated use of choral reading with filtered components of speech and whispered speech on the frequency of stuttering. Three passages read by a normal adult male were lowpass filtered with kneepoint frequencies at 100 Hz (approximate glottal source), 500 Hz (source and first formant), and 1 kHz (source and the first two formants). Along with a whispered passage, a normal passage, and a control condition, these stimuli were used in a repeated-measures design with 12 adult stutterers as they read passages while listening to one of the stimuli. Frequencies of stuttering in each condition were analyzed. The choral speech, the 500-Hz, the 1-kHz, and the whispered speech conditions all decreased the frequency of stuttering while the 100-Hz stimuli did not. It is suggested that articulatory events, chiefly the encoded speech output from the vocal tract, create effective cues and may induce fluent speech in people who stutter.     

Toward a perceptual theory of transparency

Theories of perceptual transparency have typically been developed within the context of a physical model that generates the percept of transparency (F. Metelli's episcotister model, 1974b). Here 2 fundamental questions are investigated: (a) When does the visual system initiate the percept of one surface seen through another? (b) How does it assign surface properties to a transparent layer? Results reveal systematic deviations from the predictions of Metelli's model, both for initiating image decomposition into multiple surfaces and for assigning surface attributes. Specifically, results demonstrate that the visual system uses Michelson contrast as a critical image variable to initiate percepts of transparency and to assign transmittance to transparent surfaces. Findings are discussed in relation to previous theories of transparency, lightness, brightness, and contrast-contrast.     

Titrating-delay matching-to-sample in the pigeon

The titrating-delay matching-to-sample (TDMTS) procedure offers researchers an additional behavioral task thought to capture some important features of remembering. In this procedure, the delay between sample offset and comparison onset adjusts as a function of the subject's performance. Specifically, correct matches increase the delay and incorrect matches decrease the delay, and steady-state titrated delays serve as the primary dependent measure. The present series of experiments investigated the effects of several procedural variables on performance in TDMTS procedures in an effort to elucidate better its features to allow for more precision in future use. Experiment 1 reports results from a parametric analysis of fixed-ratio response requirements on the sample key that indicated improved remembering in the form of higher daily titrated delay values as the requirement was increased. Experiment 2 investigated the extent to which the initial delay value in each session affected session-wide delay values. Results indicated that regardless of value of the initial delay, the subjects' performances adjusted the delay values in the direction of the known baseline delay-value levels. Experiment 3 manipulated the step size by which delay values were adjusted and the results indicated that larger step sizes increased both session-to-session variability and within-session range of titrated delay values, although the average values remained approximately the same. These results suggest that the TDMTS task serves as a promising procedure to study what many refer to as memory.