Sensorimotor integration in human primary and secondary somatosensory cortices

We measured somatosensory evoked fields (SEFs) to electric median nerve stimuli from eight healthy subjects with a whole-scalp 122-channel neuromagnetometer in two different conditions: (i) 'rest', with stimuli producing clear tactile sensation without any motor movement, and (ii) 'contraction' with exactly the same stimuli as in 'rest', but with the subjects maintaining sub-maximal isometric contraction in thenar muscles of the stimulated hand. The aim was to study the role of the primary (SI) and secondary somatosensory (SII) cortices in sensorimotor integration. The amplitude of the SI response N20m did not change with coincident isometric contraction, whereas P35m was significantly reduced. On the contrary, activation of contra- and ipsilateral SII cortices was significantly enhanced during the contraction. We suggest that isometric contraction facilitates activation of SII cortices to tactile stimuli, possibly by decreasing inhibition from the SI cortex. The enhanced SII activation may be related to tuning of SII neurons towards relevant tactile input arising from the region of the body where the muscle activation occurs.     

Effects of stimulus intensity on the lateralized readiness potential.

Information-processing models differ about whether stimulus intensity affects the speed of motor processes involved in response activation and execution. Previous studies of intensity are reviewed, but they are not decisive on this point because they have used indirect approaches requiring strong assumptions. Two experiments examined the effects of stimulus intensity on the lateralized readiness potential (LRP), a measure of hand-specific response activation. In Experiment 1, visual stimulus intensity influenced the time from stimulus onset to LRP onset but not the time from LRP onset to the keypress response. In Experiment 2, auditory stimulus intensity did not influence either of these time intervals, although it did influence the time from stimulus onset to the N100 and P300 components of the evoked potential. The results indicate that stimulus intensity does not influence the duration of motor processes in choice reaction time tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of stimulus duration and intensity on simple reaction time and response force.

Previous research indicates that response force increases with stimulus intensity in simple reaction time (SRT) tasks. This result contradicts the common view that the perceptual system activates the motor system via a punctate go signal of fixed size. An elaborated view assumes that the size of the go signal depends on stimulus intensity so that more intense stimuli yield more forceful responses. In order to examine the latter hypothesis, the present experiments manipulated stimulus duration as well as intensity. Response force increased with duration even beyond a critical value of about 60 ms at which stimulus duration no longer affected SRT. In addition, increasing the duration of a stimulus also increased the duration of force output. These findings argue against models with punctate transmission of activation to the motor system. Certain continuous models and variable output models with prolonged go signals provide acceptable accounts of these effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Proprioception in schizophrenics and normals: Effects of stimulus intensity and interstimulus interval.

Obtained weight discrimination thresholds for 18 schizophrenics and 18 normals at various levels of weight intensity and presentation interval. The discrimination performances of all Ss were evaluated in terms of Weber ratio scores and the number of correct discriminations for each test condition. Differential effects attributable to diagnosis were found, with schizophrenics performing with less accuracy than normals at the lowest level of weight intensity. The different presentation intervals did not yield significant differences in discrimination. It is concluded that there is a proprioceptive deficit in schizophrenia which is due to inadequate sensory input and not to insufficient proprioceptive memory. Signal-detection theory is acknowledged as providing a possible alternative explanation of the results. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus intensity dynamism: Effect of non-reinforcement of the highest intensity stimulus.

24 naive male albino Sprague-Dawley rats, in 2 groups, received extensive lever-pressing-discrimination training to 4 intensities of auditory stimulation (85, 90, 95, 100 db.); 1 intensity was SDELTA and 3 were SD. For 1 group, the lowest intensity stimulus was nonreinforced; for the other group the highest intensity stimulus was the SDELTA. After 24 days, nonreinforcement in each group was switched to stimulation of the other extreme and performance was assessed for an additional 15 days. Results indicate that (a) during the 1st phase response strength was a positive function of the distance, along the intensity continuum, from the nonreinforced stimulus; (b) after nonreinforcement contingencies were changed, performance was immediately disrupted and tended to be replaced by the functional relation of the initial phase; and (c) SDELTA response rate was positively related to SDELTA intensity. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preparedness and phobia: Effects of stimulus content on human visceral conditioning.

Conducted 6 experiments to test M. Seligman's (see PA, Vols 45:1675 and 48:1326) preparedness theory of phobia in human classical conditioning of skin conductance and heart rate responses with approximately 12 undergraduates. Conditioned stimuli (CSs) were photographs of plants, human artifacts, and phobia-relevant animals. Both aversive tactile and auditory unconditioned stimuli (UCSs) were assessed. Combined present results indicate that, consistent with results obtained by A. Ohman and colleagues in research conducted between 1975 and 1985 to test Seligman's theory, electrodermal extinction was slower to phobia-relevant stimuli than to other stimuli (and in the present study, was shown to depend on a tactile UCS); however, unlike the findings of Ohman and colleagues, when Ss were told that shocks would be discontinued, phobic CSs extinguished as readily as unprepared CSs. New evidence was obtained for a preparedness effect during acquisition trials: Only Ss receiving phobia-relevant stimuli developed an acceleratory cardiac conditioned response (CR). This acquisition effect was more reliable across experiments than the electrodermal extinction findings and showed less influence of CS—UCS "belongingness." Findings suggest that the preparedness effect is complexly determined and provide evidence that phobic stimuli occasion a unique pattern of conditioned visceral response. (48 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral measurement of thermal pain sensitivity in humans: Effects of stimulus intensity and instructions.

This study validated a human behavioral model of thermal nociception analogous to the rodent tail-flick assay. Effects of instructions and stimulus intensity on behavior (i.e., finger withdrawal latency) were evaluated. Using a repeated measures randomized crossover design, the authors exposed 10 volunteers to varying radiant heat intensities (from 42.2 to 52.2 degrees Celsius) during each of 4 sessions. In the different sessions, participants were told to remove their finger when they felt heat, felt unpleasant, felt pain, or could no longer tolerate pain. Withdrawal latencies significantly decreased as stimulus intensity increased and significantly increased for sensory, affective, pain, and intolerance instructions. Instruction set differences were significantly larger at higher stimulus intensities. this technique may be useful in human psychopharmacological research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of intermittent, moderate intensity noise stress on human performance.

Studied the effects of prolonged exposure to 2 noise stressors (random and patterned intermittent 0 and 85 db) on the performance of 60 male undergraduates on 3 tasks requiring different abilities (reaction time, rate control, and time-sharing). The sensitivity of alternate metrics of performance degradation was also evaluated within an analysis of covariance design. Ss were randomly assigned to the various treatments, and a series of 2 * 2 * 4 (Noise Intensity * Noise Quality * Trial Blocks) covariance analyses were carried out. The effects of random noise on performance depended on the type of task and performance measure. The reaction-time task was affected, the rate-control task was not, and the time-sharing task was affected only after continued exposure to noise. Patterned noise had insignificant effects. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Two-dimensional matches from one-dimensional stimulus components in human stereopsis

Three-dimensional visual scenes project onto the retina of the eye as two-dimensional images. The third dimension, depth, is projected as subtle differences between left and right retinal images. As early as the 1830s, stereoscopic depth perception was shown to depend on horizontal disparities between these images. To detect disparity, the visual system must match corresponding parts of the two retinal images. To identify the stimulus elements used in stereo matching, I applied a disparity-adaptation technique to visual patterns whose one-dimensional components and two-dimensional features have very different disparities. Surprisingly, the adaptors that are effective in altering depth perception appear widely separated in depth from the patterns they adapt. I conclude that stereo matching occurs in all directions of two-dimensional space and that one-dimensional components are the stimulus primitives, the fundamental elements of stereo matching. This is a reversal of the classical view of stereo correspondence as a one-dimensional (horizontal) matching of monocular two-dimensional features.     

Developmental changes in the effectiveness of stimulus intensity on infant visual attention.

Tested the hypothesis that the effectiveness of stimulus intensity declines with age. Stimulus intensity was manipulated by varying the size of pairs of bull's-eye and striped patterns. 50 infants from 6 wks to 24 wks of age were shown 18 pairs of stimuli in which there were 5 different sizes of each pattern. Infants 10 wks and younger responded on the basis of size, looking more at the larger sizes. The older Ss looked more at the bull's-eye regardless of its size or the size of the striped pattern paired with it. Possible mechanisms underlying this shift are discussed, and the concept of stimulus intensity is considered. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of cigarette smoking on electrodermal orienting reflexes to stimulus change and stimulus significance

Skin conductance responses (SCRs) evoked by novel, signal, and frequent tone stimuli were measured in 20 male heavy smokers and 10 male nonsmokers over two sessions. All smokers abstained from smoking for 12 hr prior to each session. Half of the smokers smoked a cigarette of their preferred brand prior to SCR measurement in the first session, whereas the remaining smokers smoked in the second session. Nonsmokers did not smoke. Results combined across the two sessions indicated that abstinence was associated with selective depression of SCRs to the novel tone. Separate analyses of results from each session revealed that, in the second session, SCRs to both novel and signal tones were depressed in abstinent smokers, partially replicating previous findings. By contrast, first session results showed no significant effects of smoking or abstinence. Results were interpreted in terms of nicotine's effects on nonspecific arousal, with some reservations.     

Effect of stimulus intensity on prolactin and cortisol release induced by unilateral electroconvulsive therapy

The corneal wound-healing properties of fibronectin (FN) and a fibronectin hydrolysate (FNH) have been evaluated in comparison with commonly used drugs. Nonpenetrating bilateral surgical keratectomy was performed in male albino rabbits. The left eye was treated with the active product, whereas the right eye served as a control (vehicle). The healing area was measured by planimetry after fluorescein staining at 0, 24, 48, and 72 h after keratectomy. Histological and immunohistochemical analysis of the healing process was also performed. Results were as follows: (a) Nandrolone (p < 0.005) and asiaticoside (p < 0.001), both at 10 mg/ml, in eyedrops delayed the healing process. (b) An ointment containing vitamin A and amino acids also delayed the process but at the limit of statistical significance (p = 0.055). (c) FNH (20-80 mg prot/ml) significantly improved the quality and shortened the time of the healing process at 60 mg prot/ml and above. (d) Human FN (100-800 micrograms/ml) did not affect the healing process. Immunohistochemical analysis demonstrated that FNH accelerated the appearance of endogenous FN in the damaged cornea earlier than in the control eyes. It is concluded that FNH may be useful in the management of corneal wounds, whereas the effectiveness of FN is doubtful.     

Effects of relative band intensity on prediction of protein secondary structure from CD

Increasing the magnitude of a protein CD spectrum obviously increases the magnitude of each predicted secondary structure by the same amount. However, increasing the magnitude of the negative, long-wave-length portion of a protein CD spectrum usually has the opposite effect from increasing the positive, short-wave-length portion. Thus small distortions in the CD spectra of proteins at short wavelength can have a significant effect on the analysis for secondary structure. This measurement error and its effect on the analysis are systematically investigated for 16 proteins of known structure. The results demonstrate that a two-point calibration of a CD instrument is mandatory to avoid serious errors when estimating secondary structure from protein CD spectra.     

Electrodermal activity and schizophrenia: The problem of stimulus intensity modulation.

Recent reviews on electrodermal activity and schizophrenia have cited both hyperreactivity and hyporeactivity in groups of schizophrenics. One problem concerning the interpretation of hyporeactivity is that of stimulus-intensity modulation. This problem is defined, and it is suggested that researchers interested in basic neurophysiological activity of schizophrenics employ a nonstressful experimental procedure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reaction time as a function of manifest anxiety and stimulus intensity.

"The present study was designed to investigate the relative increase in drive of anxious and nonanxious individuals as a function of different intensities of stimulation… The results indicated that both an increase in manifest anxiety and an increase in stimulus intensity were effective in increasing the speed of reaction during training, and in raising the height of the temporal gradient of response strength; neither factor was effective in steepening the slope of the gradient." 17 references. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of high intensity noise on retention.

48 male Ss practiced 3 verbal learning tasks under quiet and high intensity sound conditions (111 db. approximately flat to 6000 cps). It was concluded that: "1. Noise of the intensity and frequencies employed in this experiment does not significantly affect the recall of verbal material learned under controlled conditions. 2. The recall of material learned by means of auditory stimulation is not interfered with by noise to a greater extent than the recall of material learned by visual stimulation. 3. According to… subjective reports… the noise stimulus… aroused [disturbing] minimal reactions… . 4. Subjective reports… indicated some initial disturbances… but that adaptation was quickly achieved." (PsycINFO Database Record (c) 2010 APA, all rights reserved)