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PubMed2004

Subliminal attentional modulation in crowding condition.

In the crowding phenomenon, recognition of a visual target is impaired by other similar visual stimuli (distracters) presented near the target. This effect may be due largely to insufficient resolution of spatial attention. We showed that attention could subliminally enhance orientation selective adaptation to illusory lines in the crowding condition where target-distractor separation is beyond the limit of spatial resolution of attention. Despite the traditionally held close link between attention and awareness, here we provided evidence for subliminal attentional modulation for orientation stimuli that could not have been consciously perceived.

Adult↗
PubMed1990

Logistic analysis of the defense reaction induced by electrical stimulation of the rat mesencephalic tectum.

Subliminal and threshold functions of behavioral output to electrical stimulation of the rat mesencephalic tectum were fitted using the logistic model. The results suggest the existence of isotopic albeit anisotropic freezing and flight mechanisms in the dorsal periaqueductal gray and deep layers of the superior colliculus. Moreover, the marked parallelism of immobility and running threshold functions indicates the probable coupling of these mechanisms through a kind of negative feedback. Finally, the good fitting to the model suggests that the behavioral output to electrical stimulation of these areas follows a logistic function of the logarithm of the stimulus intensity.

Aggression↗
PubMed1993

Tibialis anterior R-1 response: physiological behaviour, normative data and clinical utility in L4-L5 radicular compression.

A modified H-reflex, known as R-1 response, was recorded in healthy subjects by averaging 200 responses from the moderately contracting tibialis anterior muscle (TA) after repetitive submaximal stimulation of common peroneal nerve. Physiological changes to different modes of stimulation and recording were studied and normative data obtained at the most reliable parameters. Subsequently, the test is applied to 36 patients with clinical and myelographic evidences of L5 or L4-L5 radicular compression (with or without S1 radicular compression). Increasing the force of muscle contraction resulted in increase in amplitude up to a certain limit, with no change in latency. Increasing the current from subliminal to submaximal stimulation caused initial increase and subsequent fall in the amplitude without change in the latency. The change in the stimulus frequency from 0.5 to 3 Hz did not alter latency or amplitude but the higher frequencies sometimes did. On changing the position of the foot from plantarflexed to dorsiflexed, an increase in amplitude and reduction in duration of the response was noted. Fifty subjects were studied using stimulus intensity just enough to produce 200-400 microV M-response, stimulus duration of 1.0 msec, stimulus rate of 3 Hz and the muscle force sufficient to keep the foot in complete dorsiflexion. The tibialis anterior R-1 response (TAR-1) could be recorded reliably from both legs in all the subjects. The take-off point was sharp and in no subject was there any difficulty in measuring the latency to onset point. On repeating the test, the onset point of the response was superimposable. Latency showed linear correlation with height and age. Among the patients, 21 out of 25 cases of unilateral (84.0%) and 10 out of 11 cases of bilateral (90.9%) radicular compression had abnormal findings. Abnormalities included significant a right-left latency difference within the normal range of absolute latencies, unilateral or bilateral prolongation of latency to onset point and attenuation or absence of the response. It was concluded that the TAR-1 is an important and reliable test for the study of functional integrity of L4-L5 spinal segments in lumbo-sacral sensorimotor root lesions.

Adolescent↗
PubMed2005

Excitability changes in human corticospinal projections to muscles moving hand and fingers while viewing a reaching and grasping action.

Excitability of the H-reflex in the relaxed flexor digitorum superficialis (FDS) muscle was tested in five subjects observing a reaching and grasping action. The amplitude of the FDS H-reflex was modulated with a peak occurring during the hand-opening phase of the observed movement. When the H-reflex was facilitated by subliminal transcranial magnetic stimulation (TMS), the modulation was larger than for an unconditioned reflex of similar size. This suggests that the primary motor cortex excitability is modulated by action viewing and reasonably causes the motoneuronal excitability changes. Moreover, motor evoked potentials (MEPs) were elicited by supraliminal TMS in FDS, flexor carpi radialis (FCR) and first dorsal interosseus (FDI) when observing the same movement. MEP amplitude was modulated in FDS with the same time-course as the H-reflex, the peak excitability occurring during hand opening. In FDI, however, the maximal excitability occurred during finger closing while in FCR no correlation was found with the movement phases. Finally the EMG activity of FCR, FDS and FDI was recorded while the subjects were actually performing a grasping movement similar to the one observed. In all subjects and for each muscle there was a clear-cut correspondence between the time-course of the excitability modulation of MEPs and the temporal pattern of EMG recruitment. In conclusion, the present study suggests that 'motor resonance' subliminally activates the same motor pathways that would be overtly recruited in each observer when actually performing the observed movement, reproducing the personal strategy adopted in the same task.

Adult↗
PubMed2004

Excitability changes in resting forearm muscles during voluntary foot movements depend on hand position: a neural substrate for hand-foot isodirectional coupling.

When associating hand and foot voluntary oscillations, isodirectional coupling is preferred irrespective of hand position (prone or supine). To investigate the neural correlates of this coupling modality, excitability of the motor projections innervating the resting forearm was tested during cyclic voluntary flexion-extensions of the ipsilateral foot. H-reflexes, in some experiments facilitated by subliminal Transcranial Magnetic Stimulation (TMS), and Compound Muscle Action Potentials (CMAPs), evoked by supraliminal TMS, were elicited in Flexor Carpi Radialis (FCR) and Extensor Carpi Radialis (ECR) muscles at five intervals during the foot movement cycle. With the hand prone, a sinusoidal excitability modulation was observed in wrist flexors and extensors, but reversed in phase: in FCR, excitability increased during plantar-flexion and decreased during dorsiflexion, while in ECR the opposite occurred. This reciprocal organisation was confirmed by the excitability modulation of CMAPs evoked simultaneously in the two antagonists. When the hand was supinated, the H-reflex modulation reversed in phase, i.e., FCR excitability increased during foot dorsiflexion and decreased during plantar-flexion. In both muscles and hand positions tested, when the muscle-to-movement phase-lag was increased by inertial loading of the foot, H-reflex excitability modulations remained phase linked to muscular contractions, not to movement. Together, these results suggest that the subliminal excitability modulation of hand movers has a common central origin with the parallel overt activation of foot movers, is reciprocally organised, and is direction- not muscle-dependent. It may therefore represent the neural substrate for isodirectional coupling of hand (prone or supine) with the foot.

Action Potentials↗
PubMed1971

The functional organization of the parasympathetic secretory innervation of the submandibular gland.

1. In cats the hypoglossal and chorda-lingual nerves were cut and their central ends sewn to the peripheral end of the latter nerve. At monthly intervals the sensitivity of the submandibular gland to a secretory agent was then estimated.2 When the supersensitivity resulting from the decentralization of the gland had been lowered to a constant level acute experiments were made. Electrical stimulation of both nerves caused secretion, which was abolished by ganglion blocking drugs and atropine.3. Simultaneous stimulation of the nerves at frequencies subliminal for each nerve did not cause any secretion.4. Stimulation of one nerve at a subliminal frequency did not increase a flow of saliva evoked by stimulation of the other nerve. However, as soon as the secretory threshold was reached, the flow was markedly accelerated, provided it was submaximal.5. In many cases stimulation of the regenerated chorda fibres at a high frequency caused a flow corresponding to the maximal secretory capacity of the gland. In some experiments this was true for the hypoglossal fibres also.6. The functional organization of the parasympathetic secretory innervation of the submandibular gland of the cat is discussed in the light of these observations.

Animals↗
PubMed1996

Effects of subliminal symbiotic stimuli on anxiety reduction.

The present study assessed the effectiveness of subliminal psychodynamic stimuli in reducing anxiety. 50 male and 50 female college students were tachistoscopically exposed to one of five stimuli: MOMMY AND I ARE ONE, DADDY AND I ARE ONE, I AM HAPPY WITH MYSELF, ONE, or a control stimulus MYMMO NAD I REA ENO. It was hypothesized that men would show a significant decrease in anxiety to the MOMMY stimulus, while women were expected to respond favorably to either the MOMMY or DADDY stimulus, or to both. Results showed that the subliminal stimuli did not produce differential effects on anxiety. This finding did not support previous claims for subliminal psychodynamic activation that the stimulation of symbiotic fantasy with the maternal figure produces positive behavioral effects. Despite this negative finding women's response to the MOMMY message was predicted by measures of self-perception.

Adaptation, Psychological↗
PubMed2004

Conflict, consciousness, and control.

To what degree is executive conflict resolution dependent on conflict awareness? A recent study by Dehaene et al. compared neural responses to conflict elicited through either visible or subliminal primes. Despite behavioral conflict effects for both prime types, neural activity in a control network including the anterior cingulate cortex (ACC) was present only for visible primes. Along with other recent results, these findings have important implications for theories on the relationship between ACC, consciousness, and cognitive control.

Awareness↗
PubMed1998

Effect of subthreshold target stimuli on event-related potentials.

OBJECTIVES: Event-related potentials (ERPs) elicited by subthreshold visual stimuli were studied to assess the relationship between unconscious cognitive processing and the electrical activity of the brain. METHODS: A new method of modified visual oddball paradigm with supraliminal and subliminal stimuli was applied. Prior to the experiment, the individual 'subjective' threshold for the conscious discrimination between frequent and target stimuli was established for each subject. Supraliminal and subliminal, frequent and target visual stimuli were then alternatively presented in random order to each subject. RESULTS: Both the individual and the grand average ERPs revealed a typical response (P3) in the parietal region after supraliminally presented target stimuli. In subliminal conditions an analogous positive deflection in the central-parietal region was observed, which was elicited by the target stimulus, but not the frequent stimulus. Its latency could be clearly distinguished from the latency of the classical P3, the time difference between the two waveforms was approximately 100 ms. RESULTS: The results of this study revealed the impact of unconscious processing to target stimuli on the configuration of event-related responses.

Adult↗
PubMed2006

Right hemispheric dominance in processing of unconscious negative emotion.

Right hemispheric dominance in unconscious emotional processing has been suggested, but remains controversial. This issue was investigated using the subliminal affective priming paradigm combined with unilateral visual presentation in 40 normal subjects. In either left or right visual fields, angry facial expressions, happy facial expressions, or plain gray images were briefly presented as negative, positive, and control primes, followed by a mosaic mask. Then nonsense target ideographs were presented, and the subjects evaluated their partiality toward the targets. When the stimuli were presented in the left, but not the right, visual fields, the negative primes reduced the subjects' liking for the targets, relative to the case of the positive or control primes. These results provided behavioral evidence supporting the hypothesis that the right hemisphere is dominant for unconscious negative emotional processing.

Adult↗
PubMed2005

On the role of mask structure in subliminal priming.

Choice reaction times to visual stimuli may be influenced by preceding subliminal stimuli (primes). Some authors reported a straight priming effect i.e., responses were faster when primes and targets called for the same response than when they called for different responses. Other authors found a reversed pattern of results. Our results suggest that the sign of the priming effect depends on mask structure. Inverse priming was obtained only for masks containing the searched-for feature even though informational content of the masks was neutral. With masks of irrelevant structure, straight priming effects were found. Thus, masks are not passive stimuli whose roles are limited to rendering the prime invisible. Processing of the mask may interact with prime and target processing. Implications of the results are discussed for two hypotheses trying to account for straight and inverse priming (the self-inhibition hypothesis and object-updating hypothesis).

Adult↗
PubMed2006

Can one suppress subliminal words?

Subliminal words cause behavioral priming, yet the depth of their processing remains debated. Using transcranial magnetic stimulation (TMS), Nakamura et al. demonstrate in this issue of Neuron that this subliminal priming effect can be selectively disrupted. Distinct TMS sites disrupt priming in lexical decision and pronunciation tasks, suggesting that task set influences subliminal processing.

Brain↗
PubMed1999

Subliminal psychodynamic activation: methodological problems and questions in Silverman's experiments.

Analyses of procedures in Lloyd H. Silverman's subliminal psychodynamic activation experiments identify problems and questions. Given the information provided, none of his experiments can be replicated, and none of his positive results were found under luminance conditions he reckoned in 1983 were typical of such outcomes. Furthermore, there is no evidence in any of his experiments that all stimuli were presented completely within the fovea, a condition critical to the production of positive findings (Silverman & Geisler, 1986). These considerations and the fact that no experiment using Silverman's procedures can yield unambiguous positive results (Fudin, 1986) underscore the need to start anew research in this area. Such research should be undertaken with a greater appreciation of methodological issues involved in exposing and encoding subliminal stimuli than that found in all but a few experiments on subliminal psychodynamic activation.

Form Perception↗
PubMed1993

Effects of anxiety and awareness on colour-identification latencies for emotional words.

A modified Stroop task was used to examine the interference effects of subliminal and supraliminal emotional words on the colour-identification latencies of high and low trait anxious subjects. The subjects were randomly allocated to either an anxiety or relaxation mood induction procedure (MIP) before the modified Stroop task. Increased trait anxiety was associated with relatively greater interference in colour-identification latencies for subliminal threat stimuli. Reduced state anxiety was associated with relatively more interference of subliminal positive stimuli (mood-congruent effect), but also with greater interference of supraliminal threat stimuli (mood-incongruent effect). The results suggest that mood-congruent effects may be mediated by automatic processes, whereas controlled processes may give rise to mood-incongruent effects.

Adult↗
PubMed2004

A temporal dissociation of subliminal versus supraliminal fear perception: an event-related potential study.

Current theories of emotion suggest that threat-related stimuli are first processed via an automatically engaged neural mechanism, which occurs outside conscious awareness. This mechanism operates in conjunction with a slower and more comprehensive process that allows a detailed evaluation of the potentially harmful stimulus (LeDoux, 1998). We drew on the Halgren and Marinkovic (1995) model to examine these processes using event-related potentials (ERPs) within a backward masking paradigm. Stimuli used were faces with fear and neutral (as baseline control) expressions, presented above (supraliminal) and below (subliminal) the threshold for conscious detection. ERP data revealed a double dissociation for the supraliminal versus subliminal perception of fear. In the subliminal condition, responses to the perception of fear stimuli were enhanced relative to neutral for the N2 "excitatory" component, which is thought to represent orienting and automatic aspects of face processing. By contrast, supraliminal perception of fear was associated with relatively enhanced responses for the late P3 "inhibitory" component, implicated in the integration of emotional processes. These findings provide evidence in support of Halgren and Marinkovic's temporal model of emotion processing, and indicate that the neural mechanisms for appraising signals of threat may be initiated, not only automatically, but also without the need for conscious detection of these signals.

Adolescent↗