Effects of nonconscious perception on motor response

Effect of subconscious changes in bodily response on thought shifting in people with accurate interoception

Our thought states shift from one state to another from moment to moment. The relationship between the thought shifting and bodily responses is yet to be directly examined. This exploratory study examined the influence of cardiovascular reactivity and interoception-sensing an internal bodily state-on the shifting of thought states. Participants (N = 100, 70 women) completed two tasks: the heartbeat counting task (HCT) and the vigilance task (VT). We assessed their interoceptive accuracy through their performance on the HCT. The VT was a simple sustained attention task in which participants pressed a key when the target stimulus appeared and were asked to report their thoughts. We presented subliminal vibration stimuli to induce alterations in heart rate (i.e., vibration block). Results showed that participants with higher interoceptive accuracy reported more continuation of self-referential thought (about past episodes and future plans regarding themselves) during the vibration block than did those with lower interoceptive accuracy. These results suggest that individuals with higher interoceptive accuracy are more likely to be influenced by their subliminal bodily response, resulting in divergent attention from the task and intermittent self-referential thought.

An Argument for Amphetamine-Induced Hallucinations in an Invertebrate

Hallucinations – compelling perceptions of stimuli that aren’t really there – occur in many psychiatric and neurological disorders, and are triggered by certain drugs of abuse. Despite their clinical importance, the neuronal mechanisms giving rise to hallucinations are poorly understood, in large part due to the absence of animal models in which they can be induced, confirmed to be endogenously generated, and objectively analyzed. In humans, amphetamine (AMPH) and related psychostimulants taken in large or repeated doses can induce hallucinations. Here we present evidence for such phenomena in the marine mollusk Tritonia diomedea. Animals injected with AMPH were found to sporadically launch spontaneous escape swims in the absence of eliciting stimuli. Deafferented isolated brains exposed to AMPH, where real stimuli could play no role, generated sporadic, spontaneous swim motor programs. A neurophysiological search of the swim network traced the origin of these drug-induced spontaneous motor programs to spontaneous bursts of firing in the S-cells, the CNS afferent neurons that normally inform the animal of skin contact with its predators and trigger the animal’s escape swim. Further investigation identified AMPH-induced enhanced excitability and plateau potential properties in the S-cells. Taken together, these observations support an argument that Tritonia’s spontaneous AMPH-induced swims are triggered by false perceptions of predator contact – i.e., hallucinations—and illuminate potential cellular mechanisms for such phenomena.

Anticipatory Vibrotactile Cueing Facilitates Grip Force Adjustment during Perturbative Loading

Grip force applied to an object held between the thumb and index finger is automatically and unconsciously adjusted upon perception of an external disturbance to the object. Typically, this adjustment occurs within approximately 100 ms. Here, we investigated the effect of anticipatory vibrotactile cues prior to a perturbative force, which the central nervous system may use for rapid grip re-stabilization. We asked participants to grip and hold an instrumented, actuated handle between the thumb and index finger. Under computer control, the handle could suddenly be pulled away from a static grip and could independently provide vibration to the gripping fingers. The mean latency of corrective motor action was 139 ms. When vibrotactile stimulation was applied 50 ms before application of tractive force, the latency was reduced to 117 ms, whereas the mean latency of the conscious response to vibrotactile stimuli alone was 229 ms. This suggests that vibrotactile stimulation can influence reflex-like actions. We also examined the effects of anticipatory cues using a set of perturbative loads with different rising rates. As expected, facilitation of grip force adjustment was observed for moderate loads. In contrast, anticipatory cues had an insignificant effect on rapid loads that evoked an adjustment within 60-80 ms, which approaches the minimum latency of human grip adjustment. Understanding the facilitative effects of anticipatory cues on human reactive grip can aid the development of human-machine interfaces to enhance human behavior.

The Minimal Time Required to Process Visual Information in Visual Search Tasks Measured by Using Gaze-Contingent Visual Masking

To estimate the minimal time required to process visual information (ie “effective acquisition time”) during a visual search task, we used a gaze-contingent visual masking method. In the experiment, an opaque mask that restricted the central vision was presented at a current gaze position. We manipulated a temporal delay from a gaze shift to mask movement. Participants were asked to search for a target letter (T) among distractor letters (L)s as quickly as possible under various delays. The results showed that the reaction times and search rate decreased when the delay was increased. When the delay was longer than 50 ms, the reaction times and search rate reached a plateau. These results indicate that the effective acquisition time during the visual search task used in the study is equal to or less than 50 ms. The present study indicates that the gaze-contingent visual masking method used is useful for revealing the effective acquisition time.

Discrepancy between reaction time and visual evoked magnetic response latency under priming

We examined effects of the interval between first (S1) and second (S2) visual stimuli, stimulus-onset asynchrony (SOA), on the cortical processing of S2 using magnetoencephalography (MEG). S1 (a circle) and S2 (a cross) were presented at the same location. When the SOA was short (33, 50, and 83 ms), the major deflection of the fields evoked in response to S2 (2M) was difficult to distinguish from that evoked by S1 (1M). However, when the SOA was long (350 and 453 ms), paired stimuli clearly evoked 1M and 2M. At a long SOA, the peak latency of 2M (around 200 ms) was significantly longer than that in the control (S2 alone) condition (around 180 ms). However, in contrast, the reaction time to S2 in all SOA conditions was significantly shortened as compared with that in the control condition, suggesting dissociation between processing in the visual cortex and motor processing.

Motor adaptation to a small force field superimposed on a large background force

The human motor system adapts to novel force field perturbations during reaching by forming an internal model of the external dynamics and by modulating arm impedance. We studied whether it uses similar strategies when the perturbation is superimposed on a much larger background force. Consistent with the Weber-Fechner law for force perception, subjects had greater difficulty consciously perceiving the force field perturbation when it was superimposed on the large background force. However, they still adapted to the perturbation, decreasing trajectory distortion with repeated reaching and demonstrating kinematic after effects when the perturbation was unexpectedly removed. They also adapted by increasing their arm impedance when the background force was not present, but did not vary the arm impedance when the background force was present. The identified parameters of a previously proposed mathematical model of motor adaptation changed significantly with the presence of the background force. These results indicate that the motor system maintains its sensitivity for internal model formation even when there are large background forces that mask perception. Further, the motor system modulates arm impedance differently in response to the same perturbation depending on the background force onto which that perturbation is superimposed. Finally, these results suggest that computational models of motor adaptation will likely need to include force-dependent parameters to accurately predict errors.

Backward-masking: The effect of the duration of the second stimulus on recognition of the first stimulus

OBJECTIVE

We recorded event-related magnetic fields following a target stimulus followed by a masking stimulus to investigate the visual backward masking effect using a helmet-type magnetoencephalography system in humans.

METHODS

In the target stimulus with masking stimulus conditions, duration of the target stimulus was constant at 16 ms, and duration of the masking stimulus was altered (16, 48 and 144 ms). The target stimulus was masked by the 144-ms masking stimulus, but not by the 16-ms masking stimulus, and was obscured by the 48-ms masking stimulus. For control conditions (Single-condition), event-related magnetic fields were recorded following the sole presentation of the masking stimulus for 32, 64 or 160 ms.

RESULTS

One major response was obtained at 180 ms after the onset of the stimulation in each condition. The equivalent current dipole of one major response was estimated to lie in the occipital lobe, but there was a relatively large inter-individual difference. There was no significant difference in latency between the target stimulus with masking stimulus conditions and Single-conditions. In the target stimulus with masking stimulus conditions with the 48- and 144-ms masking stimulus, the root mean square value did not differ from that in the respective Single-condition, while the root mean square value for the target stimulus with masking stimulus conditions with the 16-ms masking stimulus was significantly smaller than that in the Single-condition with the 32-ms masking stimulus, but not different from that in the Single-condition with the 16-ms masking stimulus.

CONCLUSIONS

The peak latency of one major response depended on the onset of the first stimulus for both the target stimulus with masking stimulus conditions and Single-condition, but the root mean square value depended on the duration of the masking stimulus. We concluded that the temporal information for the target stimulus was preserved during the masking effect, while the figural information was interrupted by the masking stimulus. Our results suggested that temporal factors for the stimulus were processed differently from those responsible for the object's recognition during backward masking.