Visual mismatch negativity is unaffected by top-down prediction of the timing of deviant events

Abstract

Visual mismatch negativity (VMMN) is an event-related brain potential component that is automatically elicited by infrequent (deviant) stimuli that are inserted among frequent (standard) stimuli (i.e., an oddball sequence). Although the elicitation of VMMN is basically determined in a stimulus-driven manner, it can be modulated by top-down control. In a previous study using a "patterned" oddball sequence, where deviant (D) stimuli were regularly inserted among standard (S) stimuli (i.e., repetitions of an SSSSD pattern), VMMN was largely reduced when participants noticed the SSSSD pattern and actively predicted both the identity and timing of the deviant stimuli compared to when they did not notice the SSSSD pattern and did not form such active prediction. The present study further investigated whether or not active prediction of only the timing of deviant stimuli is sufficient for the reduction of VMMN. With the patterned oddball sequence with one deviant (here, deviant stimuli were fixed throughout the block), VMMN was reduced when the participants noticed the SSSSD pattern and actively predicted both the identity and timing of deviant stimuli (i.e., replication of the previous finding). In contrast, with the patterned oddball sequence with two deviants (deviant stimuli were randomly varied between two possibilities), VMMN was not significantly reduced when the participants noticed the SSSSD pattern and actively predicted only the timing of deviant stimuli. These results suggest that active prediction of only the timing of deviant stimuli is not sufficient to reduce VMMN.

https://ift.tt/2rjD2aN

Multiplex immunoassay measurement of amyloid-β 42 to amyloid-β 40 ratio in plasma discriminates between dementia due to Alzheimer’s disease and dementia not due to Alzheimer’s disease

Abstract

The cerebrospinal fluid (CSF) biomarkers amyloid-β₄₂ (Aβ₄₂), total Tau, and phospho-181-Tau represent important diagnostic tools to support the clinical diagnosis of Alzheimer's disease (AD). Acquiring CSF by lumbar puncture is considered a moderately invasive procedure, while blood sampling is minimally invasive with calculable risks and can be performed by trained non-medical staff. Thus, the identification of reliable and robust blood biomarkers of AD-related neuropathology would be significantly advantageous in daily practice and would allow more patients to be screened. In this study, we performed a multiplex amyloid-β assay to simultaneously measure Aβ₄₀ and Aβ₄₂. We analyzed how well Aβ₄₀, Aβ₄₂, and the Aβ₄₂ to Aβ₄₀ ratio (Aβ_42/40) could differentiate between patients suffering from dementia either due or not due to AD. In addition, we studied different factors affecting Aβ levels in plasma. Plasma Aβ_42/40 level was significantly lower in patients with dementia due to AD than in those with dementia due to other causes. Aβ_42/40 correlated weakly between plasma and CSF, but did not differ between amyloid-PET positive or negative patients. Furthermore, we found that kidney function influences Aβ₄₀ and Aβ₄₂ plasma levels, but not Aβ_42/40 level. Liver function, age, and sex do not affect Aβ levels in plasma.

https://ift.tt/2HKPI5w

Anticipatory coarticulation in non-speeded arm movements can be motor-equivalent, carry-over coarticulation always is

Abstract

In a sequence of arm movements, any given segment could be influenced by its predecessors (carry-over coarticulation) and by its successor (anticipatory coarticulation). To study the interdependence of movement segments, we asked participants to move an object from an initial position to a first and then on to a second target location. The task involved ten joint angles controlling the three-dimensional spatial path of the object and hand. We applied the principle of the uncontrolled manifold (UCM) to analyze the difference between joint trajectories that either affect (non-motor equivalent) or do not affect (motor equivalent) the hand's trajectory in space. We found evidence for anticipatory coarticulation that was distributed equally in the two directions in joint space. We also found strong carry-over coarticulation, which showed clear structure in joint space: More of the difference between joint configurations observed for different preceding movements lies in directions in joint space that leaves the hand's path in space invariant than in orthogonal directions in joint space that varies the hand's path in space. We argue that the findings are consistent with anticipatory coarticulation reflecting processes of movement planning that lie at the level of the hand's trajectory in space. Carry-over coarticulation may reflect primarily processes of motor control that are governed by the principle of the UCM, according to which changes that do not affect the hand's trajectory in space are not actively delimited. Two follow-up experiments zoomed in on anticipatory coarticulation. These experiments strengthened evidence for anticipatory coarticulation. Anticipatory coarticulation was motor-equivalent when visual information supported the steering of the object to its first target, but was not motor equivalent when that information was removed. The experiments showed that visual updating of the hand's path in space when the object approaches the first target only affected the component of the joint difference vector orthogonal to the UCM, consistent with the UCM principle.

https://ift.tt/2rk6zB8

Stimulus duration has little effect on auditory, visual and audiovisual temporal order judgement

Abstract

Some classical studies on temporal order judgments (TOJ) suggested a single central process comparing stimulus onsets across modalities. The prevalent current view suggests that there is modality-specific timing estimation followed by a cross-modal stage. If the latter view is correct, TOJ's may vary depending on stimulus modality. Further, if TOJ is based only on onsets, stimulus duration should be irrelevant. To address these issues, we used both unisensory and multisensory stimuli to test whether unisensory duration processing influences cross-modal TOJ's. The stimuli were auditory noise bursts, visual squares, and their cross-modal combinations presented at 10, 40 and 500 ms durations, and various stimulus onset asynchronies. Psychometric functions were measured with an identical task in all conditions: On each trial, two stimuli were presented, one to the left, the other to the right of fixation. The participants judged which one started first. TOJ's were little affected by stimulus duration, implying that they are mainly determined by stimulus onsets. Throughout, the cross-modal just noticeable differences were larger than the unisensory ones. In accordance with the current view, our results suggest that cross-modal TOJ's require a comparison of timing after modality-specific estimations.

https://ift.tt/2KuZZAJ

Effects of saccade training on express saccade proportions, saccade latencies, and peak velocities: an investigation of nasal/temporal differences

Abstract

Express saccades have very short latencies and are often considered a special population of saccadic eye movements. Recent evidence suggests that express saccade generation in humans increases with training, and that this training is independent of the actual saccade vector being trained. We assessed the time course of these training-induced increases in express saccade generation and how they differ between the nasal and temporal hemifields, and second whether they transfer from the trained to the untrained eye. We also measured the effects of training on saccade latencies more generally, and upon peak velocities. The training effect transferred between the nasal and temporal hemifields and between the trained and untrained eyes. More surprisingly, we found an asymmetric effect of training on express saccade proportions: Before training, express saccade proportions were higher for saccades made into the nasal hemifield but with training this reversed. This training-induced asymmetry was also observed in overall saccade latencies, showing how training can unmask nasal/temporal asymmetries in saccade latencies. Finally, we report for the first time that saccadic peak velocities increased with training, independently of changes in amplitude.

https://ift.tt/2rk6nBU

A “matched” sensory reference can guide goal-directed movements of the affected hand in central post-stroke sensory ataxia

Abstract

Patients with central post-stroke sensory ataxia (CPSA) suffer from not only somatosensory dysfunction but also the ataxic movement disorder of the affected limb. These sensory and motor impairments possibly interfere each other, but such interference is still unclear. We evaluated smoothness of grasp movements in CPSA patients using a kinematic analysis, and verified the effect of somatosensory reference from the intact hand on grasp movements. Eight CPSA patients were enrolled. We recorded their reach-and-pinch movements of both affected and intact hands toward the tip of the 3-cm-diameter vertical bar, using a three-dimensional measurement system. When executing these movements of one hand, the patients simultaneously pinched the same diameter bar as the goal tip (matched-reference condition: Matched-Ref) or the 5-cm-diameter thicker bar (mismatched-reference condition: Mismatched-Ref) by the other hand. The normalized jerk index (i.e., movement smoothness) of the affected hand was disturbed compared with the intact hand. The kinematic data of the finger opening and closing phases were also disturbed. These disturbances were partially improved with Matched-Ref but not Mismatched-Ref of the intact hand. We successfully evaluated the features of CPSA, indicating that the somatosensory reference method could be useful for rehabilitation in sensory ataxia.

https://ift.tt/2HPRnXG

Effect of high‐amylose corn starch addition on canning of yellow alkaline noodle composed of wheat flour and microbial transglutaminase: Optimization by RSM

Food Science &Nutrition, EarlyView.


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