The effects of pattern shape, subliminal stimulation, and voluntary control on multistable visual perception.

Spontaneous figure reversal of ambiguous patterns was analyzed in humans. A) With Necker-"cube"-like, or "drum"-like figures, having square or round shaped "front" and "rear" surfaces, and either large or small "depth", the perceptual intervals corresponding to both interpretations of "drum" were longer than those of "cube"; the perceived "depth" of the figures was less relevant for reversal timing (inter-reversal intervals were only slightly longer for the "deeper" figures). Although the shape of "front" and "rear" surfaces is not a crucial geometrical feature for figure reversal, it did influence its timing. More, or longer information-processing steps should probably be needed for perceptual representations of curvilinear patterns in comparison with rectangular ones. The underlying neural mechanisms are probably located at a relatively peripheral level in the visual system. B) With a modified Necker "cube"-like figure, having the two internal vertices coincident, and the long axis of the figure aligned horizontally, the effect of voluntary control on perception-reversal timing overcomes opposite effects due to either fixation-attention to pattern's focal zones, or subliminal stimulation by the pattern's biased versions, suggesting one or the other perception's possibility, while it is enhanced by concordant imagery. Voluntary control should intervene downward at a high-level processing, and should probably affect both a decision-making and a perception-stabilizing mechanism in the process of the pattern's unconscious interpretation. Results A and B are confronted with other results on both perceptual and binocular rivalry of up-to-date literature, in the frame of discussions on low-level bottom-up automatic stimulus-driven processing vs high-level top-down covert attention-driven processing.

Pre-attentive discriminability of sound order as a function of tone duration and interstimulus interval: a mismatch negativity study.

The present study addressed the pre-attentive processing of sound order. Event-related potentials were recorded from reading subjects while they were presented with pairs of two tones differing from each other in frequency (1000 vs. 1500 Hz). The within-pair (silent) interstimulus interval (ISI) was, in separate blocks, varied between 0 and 245 ms to determine the minimum separation in time needed for detecting the reversed order of the two frequencies. In standard tone pairs (p = 0.9), the frequencies were in an ascending order, whereas in the deviant pairs (p = 0.1), their order was reversed. Tone durations of 5 and 20 ms were employed in separate experiments. With the 20-ms stimulus duration, the change-specific mismatch negativity (MMN) component was elicited with all within-pair ISIs employed (0, 10, 30, 90 ms). With the 5-ms stimulus duration, however, MMN was elicited only with the 245-ms ISI but not with 95-ms or shorter ISIs. These results show that increased stimulus duration considerably improves perceiving the order of two tones at the pre-attentive level. They also indicate that the accuracy of the processing of temporal information can be probed with MMN. This finding, together with the fact that MMN elicitation does not require the subject's voluntary attention, suggests that MMN might be used in the assessment of temporal processing deficits in clinical disorders in which patients are not motivated or able to give their verbal or motor response.

Apomorphine does not influence olfactory thresholds in Parkinson's disease.

In order to verify the presumed dopaminergic basis of olfactory dysfunction in Parkinson's disease (PD), we studied olfactory functions in 12 PD patients (mean age 60.1 yrs, mean duration of PD 9.0 yrs, mean Hoehn and Yahr score 2.8) before and after apomorphine (APO) administration. Amylacetate (banana smell) in 12 sequential dilutions (in 50% steps) was used for the examination of olfactory thresholds. The testing showed no significant differences in any olfactory parameters before and after APO. Furthermore, when analysing the subgroup of 7 hyposmic PD patients, we also found no significant differences before and after APO. We therefore believe that olfactory dysfunction in PD is not dependent on dopamine deficiency.

Spatiotemporal masking in pure olfaction.

In olfaction, it is not possible to determine which nostril is being stimulated, i.e., lateralize, when a pure olfactory substance, e.g., phenylethyl alcohol or vanillin, is administered into one nostril, and, simultaneously, an odorless, solvent blank into the contralateral nostril. We subjected volunteers to extensive training, with feedback on each trial, in an attempt to determine whether it was possible, in these well-trained subjects, to overcome this apparent impossibility. We failed to obtain any evidence to support the notion that a pure olfactory stimulus could be lateralized when the odorant and blank were presented simultaneously. The task, however, became simple when the odorant and the blank entered each nostril sequentially. We investigated, using a two-channel olfactometer, temporal parameters that enabled such discrimination. We controlled the duration of odorant and blank air puffs, as well as their mutual timing, to determine the threshold stimulus onset-disparity, i.e., the interval between stimulus onset and blank onset, that resulted in an inability to lateralize. Latencies shorter than the threshold interval would be perceived as simultaneous stimulation. We determined that the onset interval was between 200 and 400 ms, depending on the duration of the stimuli (a shorter interval was noted for stimuli of 150-ms duration relative to 300- and 450-ms stimuli). This was also true when two odorants were applied, rather than an odorant and a blank, and the subject was instructed to focus on the sequence of odorant delivery and side of stimulation. The temporal onset threshold was the same for lateralization and for order of stimulation. Whether the olfactory system per se mediates this discrimination or whether inputs from olfaction and chemesthesis, via trigeminal free nerve endings stimulated by air-stream onset, combine to allow this discrimination has yet to be determined.

Gamma activity in the piriform cortex and behavioral thresholds for electrical stimulation in the olfactory bulb.

The olfactory bulb was stimulated by trains of electrical pulses in freely moving rats. Evoked responses resembling damped oscillations at the gamma frequency of 30-60 Hz were recorded in the anterior and posterior piriform cortex. Different types of unconditioned sniffing were induced by stimulation of the olfactory bulb. They were similar to those evoked by an odorant (amylacetate) but differed from the behavioral patterns evoked by non-olfactory (auditory) stimulation. Rats were trained to avoid foot-shocks following electrical pulses into the olfactory bulb as conditioned stimulus in a two way shuttle-box paradigm. Threshold electrical intensities for inducing evoked responses in piriform cortex, unconditioned behavior, and learned avoidance were compared. Thresholds for unconditioned and conditioned behavior were significantly higher in comparison with those for evoking gamma discharges in anterior and posterior piriform cortex. The results suggest that fast time-locked synchronization in the gamma range in the piriform cortex induced by synaptic input from theolfactory bulb is not sufficient for inducing corresponding behavior. Thus behavioral detection and probably also olfactory recognition do not seem to be direct consequences of this fast time-locked neural synchronization. Additional neuronal processes that are connected with further elevation of stimulation intensity seem to be necessary for that.

Manual tracing efficiency contingent upon stimulus shape and performance practice.

Tracing movements (hand-following the stationary contours of three two-dimensional figures: square, triangle and circle by means of a computer mouse-operated lightspot) were analyzed during five consecutive days. All three figures consisting of four (square, circle) or three (triangle) segments had the same circumference. Three parameters were chosen to express the tracing efficiency: average error, average time and performance quotient (average error per time unit) either for individual segments or the whole figures. The performance quotient was the best for the square and the worst for the circle, yielding better values for horizontal (than for others) segment orientation for the square and triangle. On the contrary, vertical segment orientation was found to be the best for the circle. The performance quotient and average error yielded better values in triangle segments when the right hand was used (all subjects were right-handed). However, considering the whole figures all three parameters displayed better values for the right hand. No differences were found with respect to the direction of tracing movements (clockwise or counter-clockwise). During the first three days both average error and time decreased, the change in later performance is caused by shortening of the average time only.

Changing difficulty level in a one-dimensional tracking task and corresponding heart rate changes.

Subjects were required to track a target consisting of two vertical bars moving with either a constant or a sinusoidally modulated speed across an oscilloscope screen with a joystick-controlled light-spot. Either target size (distance between bars-size guided tasks) or velocity of the target movement (velocity guided tasks), varied throughout different tasks determined by subject's performance. The target's initial movement period was either 2 or 3 seconds. The following parameters were studied: time on-target intervals, time off-target intervals, number of tracking errors, heart rate and tracking error incidence over the cardiac cycle. Time on-target intervals were longer for the velocity guided tasks than for the size guided ones. The same was true for time off-target intervals. Values for both types of intervals decreased gradually over the fixed sequence of tasks for velocity but not for size guided tasks. Heart rate was higher in the size guided task. Tracking error incidence did not depend on the phase of cardiac cycle.

Sensorimotor synchronization: motor responses to pseudoregular auditory patterns.

Musically trained and untrained subjects (N = 30) were asked to synchronize their finger tapping with stimuli in auditory patterns. Each pattern comprised six successive tonal stimuli of the same duration, the first of which was accented by a different frequency. The duration of inter-stimulus onset intervals (ISIs) gradually increased or decreased in constant steps toward the end of the patterns. Four values of such steps were used in different trials: 20, 30, 45, and 60 msec. Various time-control mechanisms are hypothesized as being simultaneously responsible for subjects' incorrect reproduction of the internal temporal ratios of the stimulus patterns. The mechanism of assimilation (of a central tendency) led subjects to enforce a regular (isochronous) structure on the patterns. The influence of other time-control mechanisms (distinction, subjective expression of an accent, sequential transfer) was expressed mainly in differences between intertap onset intervals (ITIs) and the corresponding ISIs at the beginning of the patterns. The duration of the first two ITIs was in the majority of the trials in an inverse ratio to the ratio of the respective ISIs. The distortions resulting from the timing mechanisms concerned were more pronounced in the performance of nonmusicians than in that of musicians.

Temporal integration in sensorimotor synchronization.

Abstract The concept of a temporal integration process in the timing mechanisms in the brain, postulated on the basis of experimental observations from various paradigms (for a review see P$oUppel, 1978), has been explored in a sensorimotor synchronization task. Subjects synchronized their finger taps to sequences of auditory stimuli with interstimulus-onset intervals (ISIs) between 300 and 4800 msec in different trials. Each tonal sequence consisted of 110 stimuli; the tones had a frequency of 500 Hz and a duration of 100 msec. As observed previously, response onsets preceded onsets of the stimuli by some tens of milliseconcls for ISIs in the range from about 600 to 1800 msec. For ISIs longer than or equal to 2400 msec, the ability to time the response sequence in such a way that the response 5 were placed right ahead of the stimuli started to break clown, i.e., the task was fulfilled by reactions to the stimuli rather than by advanced responses. This observation can he understood within the general framework of a temporal integration puce 55 that is supposed to have a maximal capacity (integration interval) of approximately 3 sec. Only if successive stimuli fall within one integration period, can motor programs be initiated properly by a prior stimulus and thus lead to an appropriate synchronization between the stimulus sequence and corresponding motor acts.

Extralemniscal co-activation is not indispensable for behavioral detection of auditory stimuli.

Thresholds for triggering summed auditory evoked responses (ERs) were measured in non-auditory (= extralemniscal--EL) nuclei receiving direct auditory projections from the lateral lemniscus. Primary EL ERs with onset latency of 3-6 ms reflecting activation of direct EL projections of lemniscal auditory nuclei were registered in caudal pontine reticular nucleus (CPRN), in deep layers of superior colliculus (SC) and in ventromedial hypothalamus (VMH). Secondary EL ERs (waves of EL ERs with onset latency above 10 ms) reflecting diffuse auditory EL co-activation of the brain, were registered besides the above mentioned nuclei also in the medial amygdala (MA). Threshold sound intensities for evoking primary EL ERs in CPRN, SC and VMH, for secondary EL ERs in all extralemniscal nuclei tested, and for conditioned avoidance behavior in a two-way shuttle box, were compared mutually. There were no significant mutual differences among thresholds for inducing secondary EL ERs in all EL nuclei tested. Thresholds for evoking secondary EL ERs were lower than those for evoking primary EL ERs in deep layers of the SC, equaled to thresholds for primary EL ERs in the VMH and were higher than thresholds for primary EL ERs in the CPRN. The results suggest that auditory EL projections into SC and/or VMH (but not into CPRN) might represent the primary triggering source for secondary EL ERs in various extralemniscal nuclei. Although conditioning lowered the threshold intensities for inducing secondary EL ERs, the threshold sound intensity for triggering conditioned behavior was lower than the threshold for secondary EL ERs.(ABSTRACT TRUNCATED AT 250 WORDS)

EEG changes related to one-dimensional hand-tracking.

Central and occipital EEGs were recorded during one-dimensional eye-hand tracking in humans. A negative slow potential shift followed the commitment of tracking errors at electrode O1 and their correction both at O1 and C3. Error commitments were also followed by a relative decrease in alpha and beta-band power at O1, whereas their corrections followed a decrease in beta-band power at O2 and C3.

Auditory-evoked responses influenced by presence or absence of EEG alpha activity and actual cognitive state.

The presence or absence of alpha activity in occipital EEG was detected automatically. Auditory-evoked responses (AERs) related to these two brain states and at the same time to different perceptual-cognitive situations (passive listening, discrimination between two tones and pressing the button accordingly similar discrimination without motor reaction) were analyzed and compared statistically. The main result was that during the alpha state (and not during the non-alpha state, when EEG was desynchronized), the amplitudes of N1, P1 waves and peak-to-peak amplitudes N1-P2 were higher during passive listening to stimuli in comparison with the active perceptual-cognitive states mentioned. No differences in latencies of AERs were found.

Cooperative tapping: time control under different feedback conditions.

The same isochronous tone sequence was presented simultaneously to two mutually isolated subjects. In half the trials, accentuation in this sequence was accomplished by doubling the duration of the first and then of every fourth tone; in the other half, by doubling the frequency of those tones. The subjects' task was to follow the rhythm of the resulting four-tone patterns by finger tapping to tone onsets. There were four auditory feedback (FB) conditions: (1) no FB; (2) FB from the subject's own motor responses; (3) "alien" FB from the motor responses of the other pair member who, in turn, was listening to FB from his/her own tapping; (4) mutually "crossed" FB, where each pair member listened to FB from the tapping of the other. Tap onsets regularly preceded stimulus onsets. The observed order of the amount of this anticipation (from least to greatest) was: (1) own FB, (2) no FB, (3) alien FB, and (4) crossed FB. No mutual dynamic influence between simultaneously performing subjects was detected. Anticipation was more pronounced for sequences that were accentuated by frequency rather than by duration changes. The type of accent also influenced timing of intertap intervals in the rhythmic patterns. For the frequency accent, regular timing was produced, whereas for the durational accent, shortening of the second and lengthening of the fourth (the last) intertap interval were observed. The presence and source of feedback as well as the character of accentuation are therefore relevant factors in the timing of auditorally controlled rhythmic motor behavior.

Perceptual-motor coordination and style in healthy boys and those with minimal brain dysfunction.

Differences in visual-motor tracking by 8- to 9-yr.-old boys diagnosed with Minimal Brain Dysfunction or healthy have been analyzed. The subject's task was to use two computer keys to control a cursor line within a target which moved horizontally in two directions over the display. Target size and speed were the experimental variables. Off-target incidences and durations were measured and evaluated. The latter were longer and the former were more frequent on small targets for boys with brain dysfunction than for healthy boys. The two measures correlated negatively in most situations. The perceptual-motor style expressed by means of the distribution of coincidences of the two measures being over or under a criterion set equal to the corresponding averages of the healthy boys was different in the two groups. Brain-damaged boys were characterized mostly by the combination of high incidence of low duration misses for small and fast targets and by high incidence of high duration misses for large and slow targets, whereas most healthy boys showed a few misses of low duration for large and slow targets and few misses of high duration for small and fast targets.

Perception of timing of movement-onset in a simple reaction time task.

Subjects judged verbally on temporal order between pressing a switch and a marking sound (MS) in a simple reaction time paradigm. They were uncertain when sound preceded movement by less than about 60 ms or followed it by less than 130 ms (transient zone--TZ). The point of subjective equality (defined by 0.5 probability of correct judgements of temporal order of sound and switching onsets) and the median of TZ were shifted about 60 and 35 ms prior movement onset, respectively. Estimating mutual timing of movement preparation and execution and sensory delays, these shifts correspond to the simultaneity of onsets of MS and proprioceptive feedback in the brain. Thus the results suggest about proprioceptive origin of perception of active movement onset.

Increase in cutaneous temperature induced by hypnotic suggestion of pain.

Eight patients with atopic eczema and six healthy subjects were given hypnotic suggestion to feel pain in the upper part of the back and in one case on the palm. An average local increase in skin temperature of 0.6 degrees C (detected by thermovision) occurred under this condition. For some patients cutaneous pain threshold was increased before the experiment by means of repetitive hypnotic suggestion of analgesia. These subjects reported feeling no pain subjectively, but the local change in skin temperature was equal in both cases. The results suggest a central mechanism induced by measuring changes in pain threshold in the skin, which changes are independent of local changes in blood flow.

Two-dimensional manual tracking of periodic movements: event and time interval analyses.

Human visuo-motor functions were analysed by means of two-dimensional manual tracking tasks. A computer-based system for visual target generation, its movement control and real-time evaluation of the subjects' performance was developed. Various types of two-dimensional periodic target movements (over circular and square trajectories with different velocities) and various settings of tracking spot-joystick relation (normal and reversed direction) were used. Tracking success was expressed in terms of: (a) incidence of tracking errors; and (b) time spent within target. Results from the experiments performed with healthy non-trained subjects have demonstrated that tracking success is lower for a square target trajectory than for the circular one, and for higher target velocity than for the lower one. Reversed two-dimensional tracking was found to be very difficult. The results based upon the two criteria of tracking success (a,b) were different for the majority of tracking variants adopted. Quantitative and qualitative differences among subjects in tracking success were found. Two-dimensional target movements were substantially more difficult than one-dimensional ones with comparable parameters (analyzed in a previous paper).

Hippocampal auditory evoked response threshold in the rat: behavioral modulation.

Summed auditory evoked responses (AERs) were recorded bipolarly from CA1 field and inner molecular layer of the dentate gyrus of the hippocampus (Hipp) and compared to AERs simultaneously recorded from other extralemniscal (EL) nuclei and the inferior colliculus (IC) in the rat. There were no significant threshold differences for early Hipp AER (EHAER) and other EL AERs. The threshold for EHAERs and other EL AER was by several tens of decibels above that for IC, but usually lower than that for eliciting muscular reflexes. Actual behaviour (still waking, drowsiness, exploration, attention to stimuli) modified the thresholds for EHAER and other EL AERs equally. There was only little effect of actual behavior upon nonthreshold modulation of amplitudes of EHAERs. It is assumed that setting the threshold of the hypothetical common source of EH and other EL AERs plays main role in their behavioral modulation. As supposedly EHAERs are mediated through the perforant path, our results suggest that this pathway might transmit information related to high-threshold diffuse activation of the brain during the early stage of auditory processing.