Dyssynchronous apraxia: failure to combine simultaneous preprogrammed movements

Limb apraxia, a defect in skilled, learned purposive movement, may be related to impairment of either representational or innervatory components of praxis processing. Innervatory motor patterns, in turn, may involve on-line motor programs (visual feedback-controlled) or prepared movement programs (independent of continuous visual feedback). We evaluated movement abilities ofthe innervatory pattern system in TB,a 26-year-old patient with apraxia from a left dorsolateral frontal stroke. TB and four controls performed nonmeaningful single and multi-joint movements to command, with multi-joint movements combined sequentially (e.g. "open and close your hand and then bend your elbow") or simultaneously (e.g. "open and close your hand; keep doing that while bending your elbow"). TB showed no difference between single-joint (71.5% correct) and multi-joint movements in sequential combinations (68% correct), but she was significantly worse at simultaneous movement combinations (28.6% correct; P < .02). Controls performed consistently at > 90% mean accuracy. TB and four normals also performed the Fitts (1954) task, in which they alternately tapped with a pen between two target circles of varying size. TB was proportionately slower than controls on the larger Fitts circles, which call predominantly on prepared movement programs; her performance on the smaller circles (involving more on-line programs) was comparable to normals. We conclude that functional synchrony of one innervatory pattern subtype, prepared movement programs, may require late-level frontal processing, and that failure at this level can result in both apraxia and defective programming of nonmeaningful movements.     

Sensitivity to masked conditioned stimuli predicts conditioned response magnitude under masked conditions

Expression of conditioned fear has been reported to be independent of perceptual awareness of conditioned stimuli (CSs). Previous studies have been criticized, however, for not adequately assessing perceptual awareness. We fear-conditioned participants to one of two symbols and measured skin conductance responses to dichoptically masked and unmasked CSs. Participants also performed a target detection task and sensitivity (d') to the masked conditioned stimuli (CS+, CS-) was measured. Results showed that sensitivity under masking conditions was related to conditioned responses to masked CSs but not unmasked CSs. Thus, a strong relationship between expression of conditioned fear and awareness of the CS+ emerges when the latter is assessed by signal detection methods. Without consensus on how awareness should be defined, these findings bring balance to previous studies that have typically used less sensitive assessments of awareness.     

Affective reactions to acoustic stimuli

Emotional reactions to naturally occurring sounds (e.g., screams, erotica, bombs, etc.) were investigated in two studies. In Experiment 1, subjects rated the pleasure and arousal elicited when listening to each of 60 sounds, followed by an incidental free recall task. The shape of the two-dimensional affective space defined by the mean ratings for each sound was similar to that previously obtained for pictures, and, like memory for pictures, free recall was highest for emotionally arousing stimuli. In Experiment 2, autonomic and facial electromyographic (EMG) activity were recorded while a new group of subjects listened to the same set of sounds; the startle reflex was measured using visual probes. Listening to unpleasant sounds resulted in larger startle reflexes, more corrugator EMG activity, and larger heart rate deceleration compared with listening to pleasant sounds. Electrodermal reactions were larger for emotionally arousing than for neutral materials. Taken together, the data suggest that acoustic cues activate the appetitive and defensive motivational circuits underlying emotional expression in ways similar to pictures.     

Facial reactions to fear-relevant and fear-irrelevant stimuli

Earlier research has shown that subjects exposed to different facial expressions react spontaneously with different facial electromyographic (EMG) response patterns. In the present study subjects were exposed to fear-relevant (snakes/spiders) and fear-irrelevant (flowers/mushrooms) stimuli, while facial EMG activity, skin conductance responses (SCRs) and heart rate (HR) were measured. The stimuli evoked different response patterns. Fear-relevant stimuli elicited increased corrugator muscle activity, whereas fear-irrelevant stimuli evoked increased zygomatic muscle activity. Fear-relevant stimuli also evoked HR deceleration and larger SCR magnitudes. The present data are consistent with the theory that the face constitutes an emotional 'readout/output-system'.     

Facilitating masked visual target identification with auditory oddball stimuli

When identifying a rapidly masked visual target display in a stream of visual distractor displays, a high-frequency tone (presented in synchrony with the target display) in a stream of low-tone distractors results in better performance than when the same low tone accompanies each visual display (Ngo and Spence in Atten Percept Psychophys 72:1938?C1947, 2010; Vroomen and de Gelder in J Exp Psychol Hum 26:1583?C1590, 2000). In the present study, we tested three oddball conditions: a louder tone presented amongst quieter tones, a quieter tone presented amongst louder tones, and the absence of a tone, within an otherwise identical tone sequence. Across three experiments, all three oddball conditions resulted in the crossmodal facilitation of participants?? visual target identification performance. These results therefore suggest that salient oddball stimuli in the form of deviating tones, when synchronized with the target, may be sufficient to capture participants?? attention and facilitate visual target identification. The fact that the absence of a sound in an otherwise-regular sequence of tones also facilitated performance suggests that multisensory integration cannot provide an adequate account for the ??freezing?? effect. Instead, an attentional capture account is proposed to account for the benefits of oddball cuing in Vroomen and de Gelder??s task.     

Initiation of smooth-pursuit eye movements to first-order and second-order motion stimuli

Since normal human subjects can perform smooth-pursuit eye movements only in the presence of a moving target, the occurrence of these eye movements represents an ideal behavioural probe to monitor the successful processing of visual motion. It has been shown previously that subjects can execute smooth-pursuit eye movements to targets defined by luminance and colour, the first-order stimulus attributes, as well as to targets defined by derived, second-order stimulus attributes such as contrast, flicker or motion. In contrast to these earlier experiments focusing on steady-state pursuit, the present study addressed the course of pre-saccadic pursuit initiation (less than 100 ms), as this early time period is thought to represent open-loop pursuit, i.e. the eye movements are exclusively driven by visual inputs proceeding the onset of the eye movement itself. Eye movements of five human subjects tracking first- and second-order motion stimuli had been measured. The analysis of the obtained eye traces revealed that smooth-pursuit eye movements could be initiated to first-order as well as second-order motion stimuli, even before the execution of the first initial saccade. In contrast to steady-state pursuit, the initiation of pursuit was not exclusively determined by the movement of the target, but rather due to an interaction between dominant first-order and less-weighted second-order motion components. Based on our results, two conclusions may be drawn: first and specific for initiation of smooth-pursuit eye movements, we present evidence supporting the notion that initiation of pursuit reflects integration of all available visual motion information. Second and more general, our results further support the hypothesis that the visual system consists of more than one mechanism for the extraction of first-order and second-order motion.     

Nonconscious associative learning: Pavlovian conditioning of skin conductance responses to masked fear-relevant facial stimuli

We examined the possibility of nonconscious associative learning in a context of skin conductance conditioning, using emotional facial expressions as stimuli. In the first experiment, subjects were conditioned to a backwardly masked angry face that was followed by electric shock, with a masked happy face as the nonreinforced stimulus. In spite of the effectively masked conditioned stimuli, differential conditioned skin conductance responses were observed in a subsequent nonmasked extinction phase. This effect could not be attributed to differential sensitization or pseudo-conditioning. In the second experiment, the differential responding during extinction was replicated with angry but not with happy faces as conditioned stimuli. It was concluded that with fear-relevant facial expressions as the conditioned stimulus, associative learning was possible even in conditions where the subjects remained unaware of the conditioned stimulus and its relationship to the unconditioned stimulus.     

Facial electromyographic reactions and autonomic activity to auditory stimuli

This study explored whether high- and low-intensity auditory stimuli evoke different facial electromyographic reactions and autonomic responses. Subjects were repeatedly exposed to 95-dB and 75-dB tones (1000 Hz, 40 ms rise and fall times) while their facial electromyograms from the corrugator and zygomatic muscle regions, heart rate, skin conductance responses, skin conductance half recovery time and ratings were measured. The 95-dB tone evoked a "negative" reaction with increased corrugator activity and an autonomic response pattern that carried aspects of a defense reaction, that is, slowly habituating skin conductance responses with retarded recovery rate and an initial tendency to heart rate acceleration. Furthermore, the 95-dB tone was rated as unpleasant. The 75-dB tone elicited an orienting response indicated by a distinct heart rate deceleration and fast habituating skin conductance responses with a relatively short recovery time. Thus, the present study demonstrated that the facial electromyographic technique is sensitive to simple environmental stimuli such as auditory stimuli and that the facial response is consistent with the autonomic response patterns and the experience of the stimuli.     

Exercise effects on the time of reactions to auditory stimuli

Summary Serial response to auditory stimuli administered during dynamic physical exercise of the steady-state and non-steady-state exhaustive nature was investigated in 61 athletes. Similarly to previous studies with serial visual stimuli, auditory reaction time was found to depend on the exercise load and grew in parallel to it. The latency increase followed the character of the imposed exercise, too. In the slope of the latency increase individual and group differences were noted that, at least in part, could be explained by the existing differences in physical fitness plus motivation. Overall mean of linear correlation was 0.61 between the latency of auditory reaction and steady-state work output and 0.47 for the non-steady-state all-out efforts in our material. Reaction time tended to increase also when the effort though being constant was subjectively exhaustive during the studied duration (r = 0.46). As shown by the results, the decisive factor in this was not so much the absolute severity of work, but rather subjective fitness level. Despite that the data throughout the study were modeled by fitting a linear model, the conclusions are not contradictory to Duffy's inverted U-shape activation theory if understood in Gutin's interpretation.     

Enhancement of response times to bi- and tri-modal sensory stimuli during active movements

Simultaneous activation of two sensory modalities can improve perception and enhance performance. This multi-sensory enhancement had been previously observed only in conditions wherein participants were not performing any movement. Since tactile perception is attenuated during active movements, we investigated whether a bi- and a tri-modal enhancement can occur also when participants are presented with tactile stimuli, while engaged in active movements. Participants held a pen-like stylus and performed bidirectional writing-like movements inside a restricted workspace. During these movements participants were given a uni-modal sensory signal (visual––a thin gray line; auditory––a brief sound; haptic––a mechanical resisting force delivered through the stylus) or a bi- or tri-modal combination of these uni-modal signals, and their task was to respond, by pressing a button on the stylus, as soon as any one of these three stimuli was detected. Results showed that a combination of tri-modal signals was detected faster than any of the bi-modal combinations, which in turn were detected faster than any of the uni-modal signals. These facilitations exceeded the “Race model” predictions. A breakdown of the time gained in the bi-modal combinations by hemispace, hands and gender, provide further support for the “inverse effectiveness” principle, as the maximal bi-modal enhancements occurred for the least effective uni-modal responses.     

Differentiation of the intensity of food stimuli applied as conditioned stimuli to dogs

Summary A positive motor conditioned reflex was elaborated in 3 dogs. Pieces of meat weighing 1.5–1 g given from one plate served as a conditioned stimulus, meat from another plate served as a reinforcement. In the given conditions differentiation of the size of meat pieces proved significant. However, dogs were incapable of differentiating the same pieces of meat mixed with dough. This led to a conclusion that differentiation of meat pieces in the given conditions occurred only through the agency of distant receptors, and not of those in the oral cavity.(Presented by Active Member AMN SSSR D. A. Biryukov) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 57, No. 5, pp. 7–10, May, 1964     

Effects of trial order and differential conditioning on acquisition of differential shock expectancy and skin conductance conditioning to masked stimuli

Research suggests that when people are fear conditioned to masked spiders and snakes (electric shocks are contingent on only spiders or snakes), they acquire a conditional skin conductance response and can predict the occurrence of shocks even though they are unable to identify the masked spiders and snakes. Because in prior studies trial order was not completely random, it is unclear if findings were due to the contingencies from differential conditioning or a restricted trial order or both. When participants were assigned to four groups to disentangle effects of trial order and differential conditioning to masked pictures in acquisition, effects were obtained only for trial order. These findings demonstrate that trial order can result in conditioning. However, because effects were observed even for participants who reported unawareness of the contingency from trial order, results are consistent with the notion of hunches or gut feelings.     

Facilitation effect of auxiliary noise stimuli on response of isolated frog muscle spindle to sinusoidal movements

Receptor potentials and impulse patterns were recorded from isolated frog muscle spindles using sinusoidal and superimposed random stretches as stimuli with different sinus-to-noise ratios. The entire dynamic amplitude range of the spindle receptor was evaluated by measuring the sensory response at different levels of static stretch. Auxiliary random stimuli provoked rectified fast depolarizing receptor potential transients; their amplitude and slope grew larger with increasing intensity of the noise stimulus and with increasing prestretch level. Due to this strongly nonlinear behavior of the transducing site the frequency and size of the receptor potentials evoked by the auxiliary input signal increased during the stretching phase of the sinusoidal movement. Since the fast depolarizing receptor potential transients provided a powerful trigger for the action potential encoding site, auxiliary random stimuli effectively enhanced the afferent discharge rate, especially during the stretching phase of the sinusoidal movement. Auxiliary noise stimuli could even activate the afferent discharge to an otherwise subthreshold sinusoidal stretch. It is assumed that by the same mechanism the transfer characteristic of the receptor is broadened towards higher frequencies. Since auxiliary random stimuli increased the nonlinear properties of all receptor response components, a "linearizing" approximation technique only partially describes the receptor's transfer properties. The facilitation effect recorded in the differentiated muscle spindle when random stimuli were superimposed on sinusoidal displacements closely resembled the excitation of afferent firing when passive stretching interacted with active fusimotor innervation. A hypothesis is proposed to explain both effects by the same mechanism acting upon the transducing sensory endings: Since passive random stretches as well as active twitching of the intrafusal muscle fibers exhibited almost the same range of frequency components, we propose that both stimuli also generate the same kind of receptor potentials; namely, those fast-rising depolarization transients of the receptor potential, which vigorously drive the encoding site. In general, these experiments explain how the specific response of a neuron can be facilitated by an additional unspecific (noisy) input.     

Behavioral reactions to gustatory stimuli in young chicks (Gallus gallus domesticus)

Freely-moving, posthatch chicks were individually presented 2 concentrations each of quinine, citric acid, fructose, sucrose, sodium saccharin, and distilled water and their behavioral reactions were videotaped and analyzed. Already during the first posthatch day distinct rejection responses to quinine and citric acid could be recognized. Prolonged head shaking and beak clapping episodes were the most dominant features of these reactions. While responses to water and sweet stimuli could be interpreted as acceptance behaviors, the resolution was generally not fine enough to discriminate between reactions to the 2 different sweet concentrations of these stimuli or between them and water. When only water or sugar solutions were presented to other hatchlings in a single session, there was a suggestion of more definite acceptance behavior to some sweet stimuli as compared to water. It is concluded that the systems mediating aversive gustatory responses are present and functioning in posthatching chicks while acceptance responses, though present, are less discriminative among stimuli.     

Putaminal activity for simple reactions or self-timed movements

To examine the role of basal ganglia-cortical circuits in movement initiation, we trained monkeys to make the same arm movements in two ways-in immediate reaction to a randomly timed external cue (cued movements) and also following a variable delay without an explicit initiation signal (self-timed movements). The two movement types were interleaved and balanced in overall timing to allow a direct comparison of activity before and during the movement. Posterior putaminal neurons generally had phasic, movement-related discharges that were comparable for cued and self-timed movements. On cued movements, neuronal activity increased sharply following cue onset. However, for self-timed movements, there was a slow build-up in activity that preceded the phasic discharge. This slow build-up was time-locked to movement and restricted to a narrow time window hundreds of milliseconds before movement. The difference in premovement activity between cued and self-timed trials was present before the earliest cue-onset times and was not related to any differences in the overall time-to-move between the two types of trials. These features suggest that activity evolving in the basal ganglia-cortical circuitry may drive the initiation of movements by increasing until an activity threshold is exceeded. The activity may increase abruptly in response to an external cue or gradually when the timing of movements is determined by the animals themselves rather than an external cue. In this view, small changes in activity that occur in advance of the much larger perimovement neuronal activity may be an important determinant of when movement occurs. In support of this hypothesis, we found that even for cued movements, faster reaction times were associated with slightly higher levels of activity hundreds of milliseconds before movement.     

Beyond valence: the differential effect of masked anger and sadness stimuli on effort-related cardiac response

This experiment investigated the moderating effect of masked anger versus sadness primes on objective task difficulty's impact on effort-related cardiovascular response. Cardiovascular measures (ICG and blood pressure) were assessed during a habituation period and an easy versus difficult short-term memory task during which participants were exposed to masked emotional facial expressions. As expected, sadness primes led to stronger cardiac preejection period (PEP) responses than anger primes when the task was easy. When the task was difficult, we observed the reversed pattern. Here, anger primes led to stronger PEP reactivity than sadness primes. Heart rate responses described the corresponding pattern. The results demonstrate that masked anger and sadness primes have different effects on cardiac response in easy and difficult tasks. The effect of anger primes resembles the facilitating effect of happiness primes observed in previous studies.     

Do not prime too much: Prime frequency effects of masked affective stimuli on effort-related cardiovascular response

This experiment investigated the prime frequency effect of masked affective stimuli on effort-related cardiovascular response. Cardiovascular reactivity was recorded during a baseline period and an attention task in which either 1/3, 2/3, or 3/3 of the trials included the presentation of masked emotional facial expressions (sad vs. happy). In the resting trials participants were exposed to masked neutral expressions. As expected, and replicating previous findings (Gendolla and Silvestrini, in press), participants in the 1/3 priming condition showed stronger systolic blood pressure reactivity - indicating more effort - when they were exposed to masked sad faces than when they were exposed to masked happy faces. This effect disappeared in the 2/3 and 3/3 conditions. Findings are interpreted as demonstrating habituation effects of masked affective stimuli on effort mobilization.