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A patient with uncorrected antimetropia was found to attain motor fusion through blinking. Although this patient was also able to attain motor fusion through saccadic vergence and slow fusional vergence, he usually relied on blink vergence. In this patient, blink vergence was an efficient alternative to slow fusional vergence.
This report discusses blink-induced vertical motion of contact lenses as measured with a slit lamp. The motion seen this way represents the displacement of the lens from its position just before a blink to its position immediately after the blink. Motion amplitudes reported in the literature will be discussed in the context of a hypothesis which seeks to account for lens motion by taking into consideration the post-lens tear film characteristics, the diameter of the lens, and the geometry of the anterior segment of the eye.
BACKGROUND: Blink-induced lens movement causes a reduction in visual performance that is potentially greater with toric than with spherical soft contact lenses because of the combination of vertical lens movement and rotation. This study examined the effect of the two most common methods of toric lens stabilization (prism ballast and dynamic stabilization) on vision. METHOD: Four toric soft contact lens wearers were the subjects (astigmatic range 1.25 to 2.25 D). Stimulus presentation (10.5 cpd sine wave grafting flashed for 16 ms) occurred at specified times up to 400 ms after the blink. Contrast thresholds were determined monocularly with spectacles and the two types of contact lenses. RESULTS: For the grouped data, the prism balasted lens gave better overall visual performance than the dynamic stabilization at all times after the blink. Separate analysis of subject data suggested that this general pattern was not true for all individuals. CONCLUSIONS: Clinical evaluation of different lens designs on individual patients is required for achieving the optimum visual performance with toric soft lenses.
PURPOSE: The human corneal oxygen uptake responses associated with the static (nonblinking) and dynamic (blinking) wear of five rigid gas-permeable materials with high oxygen permeabilities were determined for three different center thicknesses and compared with the responses for the normal open eye and severe hypoxic stress (static wear of polymethylmethacrylate). METHODS: Corneal oxygen uptake rates were measured with a Clark-type polarographic electrode during two sessions with each of 10 human subjects. Measurements were made on the right eye for the normal open eye (air) and after 5 minutes of static and dynamic wear of polymethylmethacrylate and five rigid gas-permeable contact lens materials: Fluoroperm 92 (paflufocon A, Dk = 92), Fluoroperm 151 (paflufocon D, Dk = 151), 1992 Menicon SF-P (melafocon A, Dk = 102), 1995 Menicon SF-P (melafocon A, Dk = 159), and Menicon Z (tisilfocon A, Dk = 163-250). Lenses were manufactured in three different center thicknesses (0.12, 0.16, and 0.20 mm), with all other parameters remaining constant. Repeated-measures analysis of variance was used and included lens material (five levels), blinking condition (two levels), and lens thickness (three levels) as within-subject effects. RESULTS: Significant differences were found in corneal oxygen responses to lens material (p < 0.001) and lens thickness (p < 0.001), with lenses of lower oxygen permeability and thicker lenses being associated with higher oxygen uptake. No statistically significant differences were noted between static or dynamic wear of the lens materials (p = 0.59). CONCLUSIONS: For those very high Dk rigid lens materials studied here, moderate changes in lens thickness or material permeability may result in modest differences in corneal hypoxic relief, whereas blinking results in no significant improvement to corneal oxygenation.
Humans have difficulty processing more than one event at a time, as is evidenced by the attentional blink ('blink') phenomenon: the second of two targets in a visual stream of events cannot be reported accurately if it appears between 100 and 500 ms after the first. By using whole-head magnetoencephalography, we show that the probability of behaviourally failing to correctly identify the second target can be predicted from the amount of attentional resources devoted to processing the first target, as indexed by T1 activation. This important finding supports resource sharing accounts of divided attention tasks such as the 'blink'; that is, such tasks may reflect an individual processing strategy rather than an immutable structural processing bottleneck.
Numerous studies from several laboratories report that temporary inactivation of the cerebellar interpositus nucleus and regions of overlying cortex during eye-blink conditioning completely prevents acquisition of the conditioned eye-blink response (CR) without affecting the ability to learn the CR in subsequent training without inactivation. Recently, these results have been challenged by the suggestion that learning was not completely blocked in these studies. Instead, it has been suggested that low levels of responses on test sessions might represent a retarded form of learning caused by drug effects on cerebellar cortex. The present study was designed to address this issue directly. Very low doses of muscimol were used to selectively inactivate the interpositus nucleus of rabbits during five conditioning sessions. Animals performed no significant levels of CRs during those sessions. Training was continued four more sessions without any inactivations to test whether any learning had occurred during the previous five sessions. Detailed analysis of responses during session six revealed that learning was completely blocked by the low doses of muscimol infused into the interpositus during the first five sessions. Animals subsequently acquired the CR normally. These results confirm and extend the original findings that appropriate lesions (either temporary or permanent) of the interpositus nucleus completely prevent acquisition of the conditioned eye-blink response. Other issues regarding reversible inactivation studies are also discussed.
Many theories of motor learning explain learning-related changes in motor behavior in terms of plasticity in the cerebellar cortex. Empirical evidence, however, does not always appear to be consistent with such formulations. It is the anterior cerebellar interpositus nucleus (aINP) that seems to be essential for acquisition and retention of conditioned eye-blink responses under most circumstances and it has been therefore suggested that the aINP is the critical site of learning-related plasticity during eye-blink conditioning. Supporting this conclusion are studies demonstrating that multiple-unit conditioning-related neural activity patterns observed in many brain regions disappear after aINP lesion. The possibility that the cerebellar cortex may be involved in forming these patterns has not been assessed adequately, however. In the current study, trained rabbits received kainic acid lesions of the INP. After recovery, the animals underwent additional sessions of conditioning during which single-unit activity was recorded from the cerebellar cortex. Our results suggest that the aINP is not the sole site of plasticity during eye-blink conditioning, as a subset of the neurons recorded from lesioned animals demonstrated conditioning-related firing patterns. The lesions did change the character of these firing patterns from those observed in saline controls, however, in ways that can be generally described as a loss of organization. The normal tendency for the population of cortical cells to change firing rate together, for instance, was significantly less noticeable in lesioned animals. These results suggest that the aINP may be involved in the production of important features of conditioned responding, such as system timing function, therefore suggesting the need for more models that incorporate aINP and brain stem feedback as integral to the production of organized neural and behavioral responses.
Electrophysiological methods of studying the habituation of the blink reflex have been used, to document by objective means the lack of habituation of the blink reflex in mentally retarded adults. Habituation of the blink reflex to sets of stimuli with decreasing interstimulus duration, which is fixed in each set of stimuli, has been studied in normal human volunteers and mentally retarded subjects. Habituation of direct and indirect R2 has been poor or absent in the mentally retarded subjects. The habituation indices of mentally retarded subjects do not overlap the habituation indices of the normal volunteers. In significant numbers of retarded subjects no habituation of the indirect R2 (P less than 0.00001) and of direct R2 (P less than 0.0005) was noted. No significant difference in habituation of the direct R2 and indirect R2 is noted in normal volunteers.
This study was done to record the difference in habituation patterns of optically evoked blink reflexes in mentally retarded and normal adults. Sets of photic stimuli with fixed interstimulus duration were utilized in normal volunteers and mentally retarded adults. The interstimulus duration decreased with each sequential set. The blink responses were recorded on fibreoptic recording paper. These electrophysiological methods show objectively that the blink responses to light which habituate in normal adults fail to do so in those who are mentally retarded.
PURPOSE: Brain imaging studies have shown that global and local attention activate different areas of the brain, with implication for dependence of perception on attentional state. The aim of the present experiment was to investigate the duration of the attentional blink in global versus local attention. METHODS: Rapid Serial Visual Presentation (RSVP) sequences of global/local stimuli were presented to 34 adult subjects who had to identify a target red figure followed by a determination of whether a certain probe letter, 'X' (specified to be either the global or local form), was present in the subsequent string of letters. RESULTS: Attentional blinks were longer than any previously reported (1.67 s global; 2.97 s local) and were significantly different.Thus, the length of the attentional blink is dependent on the attentional state of the subject. CONCLUSION: This pattern of results is consistent with the hypothesis that global attention mechanisms receive predominantly M-pathway input.
Tourette syndrome (TS) is a common disorder which typically occurs during childhood or early adolescence. There is no definitive diagnostic test for TS. The objective of this study was to demonstrate whether neurophysiological abnormalities of the blink reflex can be observed in children with TS. We enrolled 15 children with TS, diagnosed according to DSM IV Diagnostic Criteria, and 15 controls. The blink reflex was elicited by stimulating the supraorbital nerve in order to measure the early response (R1), homolateral and contralateral R2 (late) responses, amplitude of R1 and duration of R2. The mean duration of R2 was significantly longer in TS patients than in the controls (P < 0.001, Student's t-test). An abnormal pattern of the blink reflex can be, even in childhood, an early neurophysiologic marker of TS, which is not related to the duration of TS or to the age of onset.
The onset and development of the delayed blink response, elicited by a tap to the glabella, and its modification by an acoustic stimulus (tone), were studied longitudinally in 36 healthy preterm and 43 term infants. Blink amplitude increased with gestational age. By term postconceptional age, the responses of the preterm infants to tap alone, and to both tap and tone, were not significantly different from those of the term infants. These results suggest that neurological development, as reflected by the blink reflex and its modification, proceeds in an orderly, sequential fashion and that the mechanisms affecting these brainstem processes are not altered by environmental influences.
Prepulse inhibition of the reflex blink by a weak stimulus shortly preceding a blink-eliciting stimulus has been described as a sensorimotor gating phenomenon that may protect processing of the first stimulus. To determine how a stimulus configuration that elicits prepulse inhibition also affects exogenous evoked potentials and perceived loudness of the paired stimuli, the three types of response were recorded simultaneously under four conditions: tone pairs of 75-110 dB and 75-75 dB and single control tones of each intensity. Two studies using different intrapair intervals found that blinks and exogenous potentials peaking after 50 ms were smaller for the second tone of pairs than for equal-intensity single tones. Pairing also reduced the loudness of 110-dB second tones, but the loudness of 75-dB first and second tones was unaffected or increased. These effects are discussed in terms of parallel processing of transient, unmodulated information in specific paths, steady-state modulated information in nonspecific paths, and a context-dependent effect on loudness judgments.
BACKGROUND: Lack of habituation, as reported in migraine patients between attacks for evoked cortical responses, was also recently found for the nociceptive blink reflex (nBR) mediated by brainstem neurons. It is not known if both brain stem and cortical habituation deficits are correlated in the same patient, which would favor a common underlying mechanism. OBJECTIVE: To search for intraindividual correlations between habituation of pattern reversal-visual evoked potentials and that of the nociception-specific blink reflex in migraineurs and in healthy volunteers (HV). METHODS: We recorded 15 HV and 15 migraine without aura patients between attacks. Habituation for visual evoked potentials was measured by comparing the N1-P1 amplitude change (%) between the first and sixth block of 100 sequential averaged responses. Habituation for the nBR was defined as the percentage change of the R2 response area between the 1st and 10th block of five averaged EMG responses, elicited by stimulating the right side every 2 minutes for 32 minutes. We also calculated the slope of N1-P1 amplitude and R2 response area changes from the first to the last response and the correlation with attack frequency. RESULTS: A significant habituation deficit in both cortical and brain stem evoked activity characterized on average the group of migraineurs compared to controls. In migraine patients, but not in HV, we found a significant positive correlation between habituation of pattern reversal-visual evoked potentials and that of the nociception-specific blink reflex both for the degree of habituation between first and last blocks of averagings (r = 0.703; P = .003) and for the habituation slope (r = 0.751; P = .001). Moreover, nBR habituation was positively correlated with attack frequency (r = 0.548; P = .034). CONCLUSION: The positive correlation between visual evoked potential and nBR habituations is consistent with the idea that in migraine the same neurobiological dysfunction might be responsible for the habituation deficit both in cortex and brain stem. As nBR habituation increases with attack frequency, its interictal deficit is unlikely to be due to trigeminal sensitization.
The relationship between tear break-up time and blink frequency was investigated in a group of 41 subjects. A significant relationship between tear break-up time and blinking was found. This suggests that tear stability plays an important role in stimulating normal involuntary blinking.
Reflexively evoked and eye-related eyelid responses were recorded using the search coil in a magnetic field technique in alert cats. The downward phase of a blink was a large (up to 21 deg), fast (up to 2000 deg s-1) eyelid displacement in the closing direction, with an almost fixed rise time duration (15-20 ms); its maximum velocity was achieved in ~10 ms. Upward eyelid motion was separated into two phases. The first phase consisted of a fast eyelid displacement, with a short duration (approximately 30 ms) and a maximum velocity up to 900 deg s-1. The second phase had an exponential-like form, lasting for 200-400 ms, and a maximum velocity ranging between 30 and 250 deg s-1. Maximum blink velocity in the downward direction was linearly related to maximum velocity of the first upward phase. The first phase in the upward direction was never observed if the eyelid stayed closed for a long period (> 50 ms) or moved slowly in the closing direction before it started to open. In these two cases, the upswing motion of the blink reflex contained only the exponential-like movement characteristic of the second upward phase, and maximum velocity in the downward direction was not related to that of the eyelid upward displacement. Mean duration of eyelid downward saccades was approximately 130 ms, and their peak velocities ranged between 50 and 440 ms. A physiological model is presented explaining the active and passive forces involved in both reflex and saccadic eyelid responses. A second-order system seems to be appropriate to describe the postulated biomechanical model.
The R2 response on the blink reflex was found to be abnormal in seven out of 17 Huntington's disease descendants. Such abnormalities were present in four untreated subjects and in three further subjects after administration of a single oral dose of levodopa-carbidopa. An increase in latency and differential latency (four cases), or in a single one of these parameters (three cases) were the abnormalities found, resembling findings in four incipient cases detected during routine family surveys. Continuous administration of levodopa-carbidopa over a 10-20 day period did not induce new characteristics in the blink reflex, nor increase those detected previously, and no case developed chorea. We suggest that the analysis of the blink reflex after a single oral levodopa-carbidopa dosage could provide an objective and quantifiable method for the detection of individuals at risk for Huntington's disease.
Reflex blinking was elicited by the electrical stimulation of peripheral nerves and various parts of the body of seven of 11 patients with Miller Fisher syndrome. This reflex blinking disappeared during recovery. Reflex blinking was elicited in normal subjects only with specific stimulation of the peripheral nerves of their upper extremities. This response may be due to a release phenomenon transmitted via the brainstem reticular formation and may be useful in detecting latent CNS involvement in patients with Miller Fisher syndrome.