Effects of visual and auditory stimuli in a choice reaction time task

The effect produced by a warning stimulus(i) (WS) in reaction time (RT) tasks is commonly attributed to a facilitation of sensorimotor mechanisms by alertness. Recently, evidence was presented that this effect is also related to a proactive inhibition of motor control mechanisms. This inhibition would hinder responding to the WS instead of the target stimulus (TS). Some studies have shown that auditory WS produce a stronger facilitatory effect than visual WS. The present study investigated whether the former WS also produces a stronger inhibitory effect than the latter WS. In one session, the RTs to a visual target in two groups of volunteers were evaluated. In a second session, subjects reacted to the visual target both with (50% of the trials) and without (50% of the trials) a WS. During trials, when subjects received a WS, one group received a visual WS and the other group was presented with an auditory WS. In the first session, the mean RTs of the two groups did not differ significantly. In the second session, the mean RT of the two groups in the presence of the WS was shorter than in their absence. The mean RT in the absence of the auditory WS was significantly longer than the mean RT in the absence of the visual WS. Mean RTs did not differ significantly between the present conditions of the visual and auditory WS. The longer RTs of the auditory WS group as opposed to the visual WS group in the WS-absent trials suggest that auditory WS exert a stronger inhibitory influence on responsivity than visual WS.

Influence of separate and mixed experimental designs on reaction times to two simple visual stimuli

Testing contexts have been shown to critically influence experimental results in psychophysical studies. One of these contexts that show important modulation of the behavioral effects of different stimulatory conditions is the separate (blocked) or mixed presentation of these stimulatory conditions. The study presents evidence that the apparent discriminabilities of two target stimuli can change according to which of these two testing contexts is used. A cross inside a ring and a vertical line inside a ring were presented as go stimuli in a go/no-go reaction time task. In one experiment, each of these stimuli was presented to a different group of volunteers and in another experiment they were presented to the same group of volunteers, randomly mixed in the blocks of trials. Similar reaction times were obtained for the two stimuli in the first experiment, and different reaction times (faster for the cross) in the second experiment. The latter result indicates that the two stimuli have different discriminabilities from the no-go stimulus; the cross having greater discriminability. This difference is however masked, presumably by the adoption of specific compensatory attentional sets, in a separate testing context.

Assimetria interlateral da atividade muscular dos membros inferiores no salto vertical / Interlateral asymmetry the activity of lower limb muscular during a vertical jump

It was investigated whether the activity of lower limb musculature shows any interlateral asymmetry during a vertical jump, namely the countermovement and impulsion phase, the flight phase, and the landing phase,were considered. These stages were represented by an initial burst of electromyographic activity, a between-bursts interval, and the first component of a final burst of electromyographic activity. Right-handed volunteers (6 male and 6 female), that practiced exercise irregularly, were tested. Electrodes were fixed over the motor point and a reference point of muscle vastus lateralis and of muscie soleus. These electrodes were connected to a standard electrophysiological recording system. The subjects performed three blocks of 1O lumps each. Individual electromyographic activity was bandpass filtered (30 to 1000 Hz) and sampled at a frequency of 3.12 5 Hz. This activity was subsequently rectified. The duration of each stage of the lump and the magnitude of each burst of activity were evaluated. These data were submitted to an ANOVA and a Newman-Keuls test, with significance level set at 0.05. Only the final burst of electromyographic activity showed interlateral differences. The duration of the first component of this activity was longer on the right side than on the left side for both the vastus lateralis muscle and the soleus muscle. The magnitude of this activity was also larger for the right side than for the left side for the vastus lateralis muscle and the soleus muscle. There is thus an asymmetric pattern of muscle activity in the inferior limb during the landing stage of a vertical jump. The right leg may be more involved in supporting the weight of the body when landing from a jump than the left leg.