Ocular abnormalities have apparent effects on brain activation. However, neuroimaging data about the ocular characteristics of healthy participants are still lacking to be compared with data for patients with ocular pathology. The objective of this multiple participants’ functional magnetic resonance imaging (fMRI) studies was to investigate the brain activation characteristics of healthy participants when they view stimuli of various shapes, pattern and size. During the fMRI scans, the participants view the growing ring, rotating wedge, fl ipping hour glass/bow tie, quadrant arc and full checker board stimuli. All stimuli have elements of black-and-white checkerboard pattern. Statistical parametric mapping (SPM) was used in generating brain activation via fi xed-effects (FFX) and conjunction analyses. The stimuli of various shapes, pattern and size produce different brain activation with more activation concentrated in the left hemisphere. These results are supported by the conjunction analysis which indicated that the left pre-central, post-central, superior temporal and occipital gyrus as well as the left cingulate cortices were involved when the participants viewed each given stimulus. Differential activation analysis showed activation with high specifi city in the occipital region due to the stimuli of various shapes, pattern and size. The activation in the right middle temporal gyrus was found to be signifi cantly higher in response to moving stimuli as compared to stationary stimuli. This confi rms the involvement of the right middle temporal gyrus in the observation of movements. The black-and-white checkerboard stimuli of various shapes, pattern and size, stationary and moving was found to 1) activate visual as well as other cortices in temporal and parietal lobes, 2) cause asymmetry in brain function and 3) exhibit functional integration characteristics in several brain areas.
Photic Stimulation

In vertebrate visual system, retina is the first stage for visual information processing. Retinal ganglion cells are the only output neurons of the retina, and their firing activities are dependent on visual stimuli. Retinal ganglion cells can effectively encode visual information via various manners, such as firing rate, temporal structure of spike trains, and concerted activity, etc. Adaptation is one of the basic characteristics of the nervous system, which enables retinal neurons to encode stimuli under a wide variety of natural conditions with limited range in their output. This article reviews the recent studies focused on the coding properties and adaptation of retinal ganglion cells. Relevant issues about dynamical adjustment of coding strategies of retinal ganglion cells in response to different visual stimulation, as well as physiological property and function of adaptation are discussed.
Photic Stimulation ; Retina ; Retinal Ganglion Cells

BACKGROUND: As the clinical-end point is not clear-cut in conscious sedation, there are no objective and feedback-providing methods to assess the depth of sedation within the levels appropriate for conscious sedation. METHODS: The investigation was carried out on 19 ASA PS 1 patients. The authors developed a system to measure the reaction time to visual (red colored flash, 40 lux for 30 msec) and auditory (beep, 1,000 Hz, 67.5 dB for 30 msec) stimulations. The authors confirmed the beeps to be audible to all the patients before the test began. When they perceived a visual or auditory stimulation, the authors instructed the patients to signal by pushing a button as soon as possible. The reaction time was defined as the time from the beginning of stimulation to the push of a button. The patients were gradually sedated with propofol TCI. The authors measured the visual and auditory reaction time and BIS after every 0.1 microgram/ml increment of the effect site concentration of propofol. RESULTS: As the effect site concentration of propofol increased, the reaction time to visual and auditory stimulations tended to be prolonged (P < 0.0001, respectively). The estimate was 409 and 498, respectively, which means the slope a in y = ax; x means unit change of the effect site concentration of propofol; y means the estimated values of the reaction time. The BIS values at loss of response to visual and auditory stimulations were 86 +/- 7 and 78 +/- 7 (mean +/- SD). CONCLUSIONS: The responses to visual and auditory stimulations were prolonged and ultimately abolished as the effect site concentration of propofol increased. The loss of response to visual stimulations preceded the loss of response to auditory stimulations. The BIS values at loss of responses to visual and auditory stimulations suggested light and moderate sedation, respectively.
Acoustic Stimulation ; Conscious Sedation* ; Humans ; Photic Stimulation ; Propofol* ; Reaction Time*

BACKGROUND: Sympathetic skin response (SSR) is a transient change in the electrical potential of the skin that is evoked by internal or external stimuli. In the present study, our purpose was to compare electrical and visual stimulation methods of evoking a SSR. METHODS: SSRs evoked by both electrical and visual stimulation were recorded from the palm and sole from 48 healthy volunteers. RESULTS: SSRs were obtained in all normal control subjects following both electrical and visual stimulation. The latency of SSR following electrical stimulation was 1383.75+/-223.56 msec at the palm and 1790.54+/-318.70 msec at the sole, and that following visual stimulation was 1518.75+/-252.64 msec at the palm and 1930.10+/-226.19 msec at the sole. The latencies of SSRs following visual stimulation were prolonged significantly more than those following electrical stimulation. The amplitudes of SSRs following visual stimulation were significantly lower than those following electrical stimulation, and the amplitude of SSRs following both electrical and visual stimulation had marked intersubject and intrasubject variabilities in each of the stimulations. CONCLUSIONS: The SSR evoked by visual stimulation is as reliable as known electrical stimulation for determining sympathetic functions and is a less invasive method. Latencies by visual stimulation are longer than those by electrical stimulation in both the palm and sole. The visual stimulation method of evoking a SSR is not influenced by an ascending somatosensory pathway theoretically, so we can postulate that it reflects a purely autonomic function if there is no problem in the visual pathway.
Electric Stimulation ; Healthy Volunteers ; Photic Stimulation ; Skin* ; Visual Pathways

ID clarify the effects of ouabain on the ERG c-wave, isolated chick retinas were exposed to different concentrations of ouabain and the results noted. Although the c-wave was abolished at a highe. dose of ouabain (10(-4)M), its amp1itude increased in the presence of ouabain at a concentration of 10(-7)M, which was within the range of clinical use of the cardiac glycoside. On the other hand, the standing potential of the retina did not change appreciably until 10(-6)M and then decreased gradually at higher concentrations.In the presence of 10(-4)M ouabain, the concentration which completely blorked Na-K-ATPase, both the c-wave and the standing potential were almost abolished. These phenomena were more conspicuous when ouabain was applied to the vitreous side rather than the choroidal side. In the presence of 10(-7)M ouabain, the light sensitivity of the retina was elevated to 0.5 log unit and the maximum response increased about 30%. This may be a sign of visual complications of ouabain, such as metachromatopsia.
Animals ; Chickens ; Electroretinography ; Ouabain/*pharmacology ; Photic Stimulation ; Retina/*drug effects

OBJECTIVE: To explore the effect of visual and haptic vertical stimulation on standing balance in post-stroke patients. METHODS: Twenty-five post-stroke patients were recruited. We measured left/right standing pressure differences and the center of pressure (COP) parameters for each patient under three different conditions: no stimulation, visual, and haptic stimulated conditions. First, patients stood on a posturography platform with their eyes blindfolded. After a rest period, the patients stood on the same platform with their eyes fixed to a 1.5-m luminous rod, which was placed at a vertical position in front of the patients. After another rest period, the patients again stood touching a vertically placed long rod in their non-hemiplegic hand with their eyes blindfolded. We collected the signals from the feet in each condition and obtained the balance indices. RESULTS: Compared with the no stimulation condition, significant improvements were observed for most of the COP parameters including COP area, length, and velocity for both the visual and haptic vertical stimulation conditions (p<0.01). Additionally, when we compared visual and haptic vertical stimulation, visual vertical stimulation was superior to haptic stimulation for all COP parameters (p<0.01). Left/right standing pressure differences, increased, although patients bore more weight on their paretic side when vertical stimulation was applied (p>0.01). CONCLUSION: Both visual and haptic vertical stimulation improved standing steadiness of post-stroke patients. Notably, visual vertical stimulation was more effective than haptic stimulation.
Foot ; Hand ; Hemiplegia ; Humans ; Photic Stimulation ; Postural Balance ; Rehabilitation ; Stroke*

Spatial frequency and direction tuning to drifting sinusoidal gratings are intrinsic properties of neurons in visual cortex neurons in areas 17 and 18. To investigate the stability of these tuning properties during visual stimulation in anesthetized cats, the temporal dynamics of spatial frequency and direction tuning were analyzed in every 0.1 sec. The responses of cortical neurons (n=109) as a function of spatial frequency as well as direction at a particular velocity for 1 second were measured and plotted as a contour plot. Five parameters from this plot were extracted: optimum response, preferred direction (direction that showed the optimum response), optimum spatial frequency (spatial frequency that showed the optimum response), direction tuning width (the difference between the highest and lowest directions to which the cell was at least half as responsive as it was to its optimum direction) and spatial frequency bandwidth (the difference between the highest and lowest frequencies to which the cell was at least half as responsive as it was to its optimum frequency). Then, this contour plot was further analyzed in every 0.1 sec to investigate whether these five parameters were changed or not during the course of stimulation. These parameters were plotted along the time (0.1 sec step) and a line of fit was found. Both spatial frequency and direction tuning properties were not changed in most of the cells. This suggests that both direction and spatial frequency tuning properties are stable during drifting sinusoidal gratings' stimulation.
Animals ; Cats ; Electrophysiology ; Neurons ; Photic Stimulation ; Visual Cortex

Attention can concentrate our mental resources on processing certain interesting objects, which is an important mental behavior and cognitive process. Recognizing attentional states have great significance in improving human's performance and reducing errors. However, it still lacks a direct and standardized way to monitor a person's attentional states. Based on the fact that visual attention can modulate the steady-state visual evoked potential (SSVEP), we designed a go/no-go experimental paradigm with 10 Hz steady state visual stimulation in background to investigate the separability of SSVEP features modulated by different visual attentional states. The experiment recorded the EEG signals of 15 postgraduate volunteers under high and low visual attentional states. High and low visual attentional states are determined by behavioral responses. We analyzed the differences of SSVEP signals between the high and low attentional levels, and applied classification algorithms to recognize such differences. Results showed that the discriminant canonical pattern matching (DCPM) algorithm performed better compared with the linear discrimination analysis (LDA) algorithm and the canonical correlation analysis (CCA) algorithm, which achieved up to 76% in accuracy. Our results show that the SSVEP features modulated by different visual attentional states are separable, which provides a new way to monitor visual attentional states.
Algorithms ; Attention ; Electroencephalography ; Evoked Potentials, Visual ; Humans ; Photic Stimulation

Brain-computer interface (BCI) systems based on steady-state visual evoked potential (SSVEP) have become one of the major paradigms in BCI research due to their high signal-to-noise ratio and short training time required by users. Fast and accurate decoding of SSVEP features is a crucial step in SSVEP-BCI research. However, the current researches lack a systematic overview of SSVEP decoding algorithms and analyses of the connections and differences between them, so it is difficult for researchers to choose the optimum algorithm under different situations. To address this problem, this paper focuses on the progress of SSVEP decoding algorithms in recent years and divides them into two categories-trained and non-trained-based on whether training data are needed. This paper also explains the fundamental theories and application scopes of decoding algorithms such as canonical correlation analysis (CCA), task-related component analysis (TRCA) and the extended algorithms, concludes the commonly used strategies for processing decoding algorithms, and discusses the challenges and opportunities in this field in the end.
Algorithms ; Brain-Computer Interfaces ; Electroencephalography ; Evoked Potentials, Visual ; Photic Stimulation

It is widely acknowledged that holistic processing is a key characteristic of face perception. Although holistic processing implies the automatic integration of face parts, it is unclear whether such processing requires the awareness of face parts. Here, we investigated the interactions between visible face parts and face parts rendered invisible using continuous flash suppression (CFS). In the first experiment with the upper half-face visible and the lower half-face invisible, the results showed that perceived face identity was influenced by the invisible lower half-face, suggesting that integration occurs between the visible and invisible face parts, a variant of the "composite face effect". In the second experiment, we investigated the influence of visible face parts on the processing of invisible face parts, as measured by the time it took for the invisible parts to break out from CFS. The results showed a visible-to-invisible facilitation effect, that the aligned invisible face parts broke through CFS faster than when the visible and invisible face parts were misaligned. Visible eyes had a stronger influence on the invisible nose/mouth than the other way around. Such facilitation of processing from visible to invisible parts was also found when Chinese characters were used as stimuli. These results show that information integration occurs across the consciousness boundary.
Awareness ; Consciousness ; Eye ; Face ; Facial Recognition ; Photic Stimulation