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Blink reflexes obtained by electrical stimulation of the supraorbital nerve and electromyographic recording of the orbicularis oculi muscle proved useful as a preliminary method in diagnosis of lesions of the brainstem and the fifth and seventh cranial nerves, and in differentiating intrinsic lesions of the brainstem from extrinsic ones. It was noted that R1 and R2 reflexes were different in the two types of lesions.
A well-established phenomenon in the study of attention is the attentional blink-a deficit in reporting the second of two targets when it occurs 200-500 msec after the first. Although the effect has been shown to be robust in a variety of task conditions, not every individual participant shows the effect. We measured electroencephalographic activity for "nonblinkers" and "blinkers" during execution of a task in which two letters had to be detected in an sequential stream of digit distractors. Nonblinkers showed an earlier P3 peak, suggesting that they are quicker to consolidate information than are blinkers. Differences in frontal selection positivity were also found, such that nonblinkers showed a larger difference between target and distractor activation than did blinkers. Nonblinkers seem to extract target information better than blinkers do, allowing them to reject distractors more easily and leaving sufficient resources available to report both targets.
BACKGROUND: The present study aimed to investigate the time course of electrocortical facilitation for affectively arousing written words during the so-called 'attentional blink' (AB) period in a rapid serial visual presentation (RSVP) task. The AB refers to a period of reduced awareness for second-target stimuli following a first target by an interval of about 200-500 ms. Pleasant, neutral, and unpleasant written verbs were used as second targets in an 8.6-Hz RSVP paradigm that contained affectively neutral words as distractors. Replicating and extending behavioral studies, we expected that emotional second targets would be associated with better identification accuracy and greater electrocortical activity, compared with neutral targets. RESULTS: The steady-state visual evoked potential was recorded using 129 scalp electrodes. The time-varying energy at the presentation frequency of 8.6 Hz was extracted as a continuous measure of electrocortical activity related to the RSVP stream. Behavioral data showed that at an inter-target interval of 232 ms, the report for emotionally arousing (pleasant and unpleasant) words was more accurate than for neutral control words. This result was mirrored by the electrocortical response at posterior sensors, which showed rapid amplitude enhancement (120-270 ms after T2 onset) for pleasant and unpleasant targets specifically. CONCLUSION: The present data suggest that identification facilitation for emotionally arousing target words in the AB is related to rapid enhancement of sensory processing. Affectively arousing information is preferentially selected at the level of early perceptual analysis, leading to facilitation at later stages of processing, including consolidation in working memory and visual awareness.
Blink reflexes were obtained in a total of 34 different patients with cerebrovascular lesions; 28 were studied within 1 week of the ictus and 11 were eventually restudied. In 13, the latency of the first component of the reflex on the clinically involved side was significantly delayed (greater than 1.5 msec). This was an acute phenomenon that usually resolved within the first week after the ictus, correlated clinically with the severity of the hemiparesis and decrease in tone, and may be seen with lesions restricted to the pyramidal tract. The second component was absent in 17 of 34 patients during the early phase after stroke, and was associated with a decreased corneal response. These changes, which reflect decreased excitability of certain brainstem structures (rather than a lesion within those structures), are therefore potentially important for documenting CNS pathophysiology.
The speckle method of characterization of multiple scattering media by squared-pulse modulation of the probe light frequency is described. This method assumes the analysis of the decay in speckle modulation that is due to the superposition of two decorrelated blinking speckle patterns. Theoretical predictions based on the phenomenological model of formation of partially blurred speckles under the condition of frequency switching are in reasonable agreement with the corresponding experimental data.
Two experiments examined the possibility that attention directed to a distractor during rapid serial visual presentation (RSVP) can produce an attentional blink (AB). A to-be-ignored distractor (D1) preceded a target word (T2) by a variable lag in RSVP streams of black false-font distractors. D1 was highlighted by color and was a word, a string of consonants, a string of digits, or a string of false-font characters. Recall of T2 was significantly suppressed at short D1-T2 lags (the AB) but only when D1 contained letters; the AB was completely absent when D1 was composed of digits or false-font characters. Thus, the AB can be triggered by a highlighted distractor if the distractor shares features with a target.
There is currently a great deal of interest regarding the possible existence of a crossmodal attentional blink (AB) between audition and vision. The majority of evidence now suggests that no such crossmodal deficit exists unless a task switch is introduced. We report two experiments designed to investigate the existence of a crossmodal AB between vision and touch. Two masked targets were presented successively at variable interstimulus intervals. Participants had to respond either to both targets (experimental condition) or to just the second target (control condition). In Experiment 1, the order of target modality was blocked, and an AB was demonstrated when visual targets preceded tactile targets, but not when tactile targets preceded visual targets. In Experiment 2, target modality was mixed randomly, and a significant crossmodal AB was demonstrated in both directions between vision and touch. The contrast between our visuotactile results and those of previous audiovisual studies is discussed, as are the implications for current theories of the AB.
When two masked targets (T1 and T2) require attention and are presented within half a second of each other, the report accuracy for T2 is reduced, relative to when the two targets are presented farther apart in time. This effect is known as the attentional blink (AB). Potter, Chun, Banks, and Muckenhoupt (1998) argued that all AB-like effects observed when at least one of the targets was presented outside of the visual modality did not represent true instances of the AB, but instead were artifacts of task-set switching. However, in the Potter et al. experiments the presence or absence of task-set switching opportunities was confounded with the T2 task, as well as the alphanumeric class of T2 with respect to the distractors. In the present experiment, we examine the influence of T1 alphanumeric class, T2 alphanumeric class, and switching operations in a fully crossed design that unconfounds these factors. In contrast to the conclusions of Potter et al., the present results suggest that the T2 alphanumeric class can account for the pattern of ABs observed across conditions, without necessarily implicating a separate switch cost. The implications for theoretical models of the AB and the debate over the validity of cross-modal ABs are discussed.
When two targets (T1 and T2) are displayed in rapid succession, accuracy of T2 identification varies as a function of the temporal lag between the targets (attentional blink, AB). In some studies, performance has been found to be most impaired at Lag 1--namely, when T2 followed T1 directly. In other studies, T2 performance at Lag 1 has been virtually unimpaired (Lag 1 sparing). In the present work, we examined how Lag 1 sparing is affected by attentional switches between targets displayed in the same location or in different locations. We found that Lag 1 sparing does not occur when a spatial shift is required between T1 and T2. This suggests that attention cannot be switched to a new location while the system is busy processing another stimulus. The results are explained by a modified version of an attentional gating model (Chun & Potter, 1995; Shapiro & Raymond, 1994).
The early (R1) and late (R2) components of the cutaneous blink reflex in right-handed humans were recorded in three experiments to examine the lateral symmetry of a simple excitatory process in their brainstem pathways and of the control of the excitability of the pathways by gaps in acoustic noise. Experiment 1 showed that a stimulus below R1-elicitation threshold increased the excitability of the right R1 pathway more than the left but that the rate of decay was similar on both sides. Experiment 2 showed that a brief unilateral gap in noise affected the R1 and R2 reflex pathways bilaterally. Experiment 3 showed that R2 varied with gap duration and that gaps to the left and right ears had indistinguishable effects. The finer temporal resolution of events in the right sensory field of right-handers seen in psychophysical judgments is not seen in the descending control of brainstem excitability.
Electrical stimulation of the supra-orbital nerve induces at the same threshold an early reflex reaction in the ipsilateral orbicular muscle and a delayed bilateral reflex response. These reflex activities are modified bilaterally by unilateral hemispheric lesions. Reactions on the hemiplegic side are reduced in amplitude, unlike the responses on the "healthy side" which are facilitated. Adaptation of the reflexogenous threshold of the delayed responses to repeated stimulation is also irregular; cumulative depression occurs earlier on the hemiplegic side, the responses on the "healthy side", on the other hand, show less habituation or a total absence of it. These electrophysiological findings agree with experimental results concerning the influence of cortical structures on the activity of the nuclei of the brain stem. They also, by analogy with the results of research carried out on the limbs, support the tactile origin of the two constituents of the blink reflex.
Computed tomography (CT) has become an important diagnostic modality in the evaluation of ocular and orbital disease. A weakness of CT, however, is its inability to show clearly intraocular lesions that do not contain calcium. These images can be improved by the careful selection of window width and window level and by the use of a technique known as "blinking." The use of these enhancement techniques is illustrated in two cases of leukocoria in children.
The present study is concerned with conditioned reflex changes in background and evoked activity of the neuronal population of the auditory cortex (AI) in three waking cats. For the elaboration of a conditioned blink reflex, a series of eight clicks was used as the signal. The unconditional stimulus was rhythmic blowing of air at the eye. During the elaboration of a positive conditioned reflex there was a significant increase in the level of background activity. During conditioned reflex extinction, background activity showed a further increase. When extinguishing inhibition became profound, it was equivalent to sleep, and there was a strong fall in the level of background activity. During the restoration of an extinguished conditioned reflex, background activity fell to the level observed during conditioned reflex extinction, at the stage of consolidation. Application of an acoustic stimulus elicited a general, sometimes a slight increase in the number of spike discharges. Within the range of 300-350 ms - the time of appearance of the evoked response - neuronal activity underwent a reorganization, sometimes with a tendency to phasic variations. Phasic variations of the given population in response to sound were observed at all stages of the study.
An electromyographic study of the blink reflex has been undertaken in the monkey Macacus cynomolgus. Reflex responses were evoked by stimulating trigeminal or facial afferent pathways and their modifications studied when a conditioning stimulus was applied to other afferences. The response may have two components (R1 = short latency, R2 = long latency) but R1 was only present after stimulating the ipsilateral supra-orbital nerve, whereas R2 alone occurred when either facial or contralateral supra-orbital nerves were stimulated. Previous stimulations of facial or contralateral supra-orbital nerves resulted in a facilitation of the reflex followed by some inhibition of R1 and R2 which became complete when the time interval was sufficient. The responses were depressed from 5 c/s (R1) or 2 c/s (R2).
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