Displaying publications 1 - 20 of 37 in total

  1. Shafie S, Kawahito S, Halin IA, Hasan WZ
    Sensors (Basel), 2009;9(12):9452-67.
    PMID: 22303133 DOI: 10.3390/s91209452
    The partial charge transfer technique can expand the dynamic range of a CMOS image sensor by synthesizing two types of signal, namely the long and short accumulation time signals. However the short accumulation time signal obtained from partial transfer operation suffers of non-linearity with respect to the incident light. In this paper, an analysis of the non-linearity in partial charge transfer technique has been carried, and the relationship between dynamic range and the non-linearity is studied. The results show that the non-linearity is caused by two factors, namely the current diffusion, which has an exponential relation with the potential barrier, and the initial condition of photodiodes in which it shows that the error in the high illumination region increases as the ratio of the long to the short accumulation time raises. Moreover, the increment of the saturation level of photodiodes also increases the error in the high illumination region.
    Matched MeSH terms: Photic Stimulation
  2. Adam A, Shapiai MI, Tumari MZ, Mohamad MS, Mubin M
    ScientificWorldJournal, 2014;2014:973063.
    PMID: 25243236 DOI: 10.1155/2014/973063
    Electroencephalogram (EEG) signal peak detection is widely used in clinical applications. The peak point can be detected using several approaches, including time, frequency, time-frequency, and nonlinear domains depending on various peak features from several models. However, there is no study that provides the importance of every peak feature in contributing to a good and generalized model. In this study, feature selection and classifier parameters estimation based on particle swarm optimization (PSO) are proposed as a framework for peak detection on EEG signals in time domain analysis. Two versions of PSO are used in the study: (1) standard PSO and (2) random asynchronous particle swarm optimization (RA-PSO). The proposed framework tries to find the best combination of all the available features that offers good peak detection and a high classification rate from the results in the conducted experiments. The evaluation results indicate that the accuracy of the peak detection can be improved up to 99.90% and 98.59% for training and testing, respectively, as compared to the framework without feature selection adaptation. Additionally, the proposed framework based on RA-PSO offers a better and reliable classification rate as compared to standard PSO as it produces low variance model.
    Matched MeSH terms: Photic Stimulation/methods*
  3. Sharanjeet-Kaur, Kulikowski JJ, Carden D
    Ophthalmic Physiol Opt, 1998 Jan;18(1):49-56.
    PMID: 9666910
    The purpose of this study was to optimise the testing paradigm for isolating the contributions of chromatic and achromatic mechanisms to the human spectral sensitivity function. Spectral sensitivity was determined for a test spot size of 1.2 deg presented with various spatial and temporal masks on a large, 10 deg background field of moderate intensity (1000 td) and colour temperature, CT = 2700 K. Sinusoidal temporal presentation (1 Hz) and a masking annulus of between 3 and 10 min of arc surrounding the test spot, was found to be most effective in separating chromatic from achromatic mechanisms. Square-wave (1 Hz) temporal presentation combined with the annulus was slightly less selective. The presence of the annulus did not affect the shape of flicker detection at 25 Hz which is a measure of the luminosity (achromatic) spectral sensitivity function.
    Matched MeSH terms: Photic Stimulation/methods
  4. Chen AH
    PMID: 12152800
    The purpose of this study was to determine if there was any difference between myopes and emmetropes in using blur as a stimulus for accommodation when the chromatic aberration, size and proximal cues were eliminated. Twenty adults (10 myopes and 10 emmetropes) were examined for their accuracy of accommodation response for five different accommodation demands (OD, 1D, 2D, 3D, 4D) under two different light sources: achromatized white light versus monochromatic light. There was no significant difference in using blur stimulus between myopes and emmetropes when the chromatic aberration, size and proximal cues were eliminated.
    Matched MeSH terms: Photic Stimulation
  5. Norhashila Hashim, Rimfiel B. Janius, Russly Abdul Rahman, Azizah Osman, Zude, Manuela, Shitan, Mahendran
    Bananas were chilled at 6oC and the appearance of brown spots when exposed to ambient air, a
    phenomenon known as chilling injury (CI), was detected using computer vision. The system consisted of a digital colour camera for acquiring images, an illumination set-up for uniform lighting, a computer for receiving, storing and displaying of images and software for analyzing the images. The RGB colour space values of the images were transformed into that of HSI colour space which is intuitive to human vision. Visual assessment of CI by means of a browning scale was used as a reference and correlation between this reference values and hue was investigated. Results of the computer vision study successfully demonstrate the potential of the system in substituting visual assessment in the evaluation of CI in bananas. The results indicate significant influence, at α=0.05, of treatment days and temperature on hue. A strong correlation was also found between hue and visual assessment with R>0.85.
    Matched MeSH terms: Photic Stimulation
  6. Lim A, Janssen SMJ, Satel J
    Cogn Affect Behav Neurosci, 2020 12;20(6):1349-1364.
    PMID: 33236297 DOI: 10.3758/s13415-020-00846-w
    Inhibition of return is characterized by delayed responses to previously attended locations when the interval between stimuli is long enough. The present study employed steady-state visual evoked potentials (SSVEPs) as a measure of attentional modulation to explore the nature and time course of input- and output-based inhibitory cueing mechanisms that each slow response times at previously stimulated locations under different experimental conditions. The neural effects of behavioral inhibition were examined by comparing post-cue SSVEPs between cued and uncued locations measured across two tasks that differed only in the response modality (saccadic or manual response to targets). Grand averages of SSVEP amplitudes for each condition showed a reduction in amplitude at cued locations in the window of 100-500 ms post-cue, revealing an early, short-term decrease in the responses of neurons that can be attributed to sensory adaptation, regardless of response modality. Because primary visual cortex has been found to be one of the major sources of SSVEP signals, the results suggest that the SSVEP modulations observed were caused by input-based inhibition that occurred in V1, or visual areas earlier than V1, as a consequence of reduced visual input activity at previously cued locations. No SSVEP modulations were observed in either response condition late in the cue-target interval, suggesting that neither late input- nor output-based IOR modulates SSVEPs. These findings provide further electrophysiological support for the theory of multiple mechanisms contributing to behavioral cueing effects.
    Matched MeSH terms: Photic Stimulation
  7. Gowen E, Jachim S, Subri S, Dickinson C, Hamblin-Pyke B, Warren PA
    Vision Res, 2020 12;177:56-67.
    PMID: 32977182 DOI: 10.1016/j.visres.2020.08.004
    Alongside difficulties with communication and social interaction, autism is often accompanied by unusual sensory and perceptual experiences including enhanced visual performance on tasks that involve separating local parts from global context. This superiority may be the result of atypical integrative processing, involving feedback and lateral connections between visual neurons. The current study investigated the integrity of these connections in autistic adults by examining two psychophysics tasks that rely on these processes - collinear facilitation and contour integration. The relative contribution of feedback and lateral connectivity was studied by altering the timing of the target relative to the flankers in the collinear facilitation task, in 16 autistic and 16 non-autistic adults. There were no significant differences in facilitation between the autistic and non-autistic groups, indicating that for this task and participant sample, lateral and feedback connectivity appear relatively intact in autistic individuals. Contour integration was examined in a different group of 20 autistic and 18 non-autistic individuals, for open and closed contours to assess the closure effect (improved detection of closed compared to open contours). Autistic individuals showed a reduced closure effect at both short (150 ms) and longer (500 ms) stimulus presentation durations that was driven by better performance of the autistic group for the open contours. These results suggest that reduced closure in a simple contour detection paradigm is unlikely to be due to slower global processing. Reduced closure has implications for understanding sensory overload by contributing to reduced figure-ground segregation of salient visual features.
    Matched MeSH terms: Photic Stimulation
  8. Battal Merlet L, Morel S, Blanchet A, Lockman H, Kostova M
    Psychiatry Res, 2014 Dec 30;220(3):752-9.
    PMID: 25240943 DOI: 10.1016/j.psychres.2014.08.034
    Schizophrenia is associated with severe episodic retrieval impairment. The aim of this study was to investigate the possibility that schizophrenia patients could improve their familiarity and/or recollection processes by manipulating the semantic coherence of to-be-learned stimuli and using deep encoding. Twelve schizophrenia patients and 12 healthy controls of comparable age, gender, and educational level undertook an associative recognition memory task. The stimuli consisted of pairs of words that were either related or unrelated to a given semantic category. The process dissociation procedure was used to calculate the estimates of familiarity and recollection processes. Both groups showed enhanced memory performances for semantically related words. However, in healthy controls, semantic relatedness led to enhanced recollection, while in schizophrenia patients, it induced enhanced familiarity. The familiarity estimates for related words were comparable in both groups, indicating that familiarity could be used as a compensatory mechanism in schizophrenia patients.
    Matched MeSH terms: Photic Stimulation/methods
  9. Yuvaraj R, Murugappan M, Ibrahim NM, Sundaraj K, Omar MI, Mohamad K, et al.
    Int J Psychophysiol, 2014 Dec;94(3):482-95.
    PMID: 25109433 DOI: 10.1016/j.ijpsycho.2014.07.014
    In addition to classic motor signs and symptoms, individuals with Parkinson's disease (PD) are characterized by emotional deficits. Ongoing brain activity can be recorded by electroencephalograph (EEG) to discover the links between emotional states and brain activity. This study utilized machine-learning algorithms to categorize emotional states in PD patients compared with healthy controls (HC) using EEG. Twenty non-demented PD patients and 20 healthy age-, gender-, and education level-matched controls viewed happiness, sadness, fear, anger, surprise, and disgust emotional stimuli while fourteen-channel EEG was being recorded. Multimodal stimulus (combination of audio and visual) was used to evoke the emotions. To classify the EEG-based emotional states and visualize the changes of emotional states over time, this paper compares four kinds of EEG features for emotional state classification and proposes an approach to track the trajectory of emotion changes with manifold learning. From the experimental results using our EEG data set, we found that (a) bispectrum feature is superior to other three kinds of features, namely power spectrum, wavelet packet and nonlinear dynamical analysis; (b) higher frequency bands (alpha, beta and gamma) play a more important role in emotion activities than lower frequency bands (delta and theta) in both groups and; (c) the trajectory of emotion changes can be visualized by reducing subject-independent features with manifold learning. This provides a promising way of implementing visualization of patient's emotional state in real time and leads to a practical system for noninvasive assessment of the emotional impairments associated with neurological disorders.
    Matched MeSH terms: Photic Stimulation/methods*
  10. Teoh SL, Allan D, Dutton GN, Foulds WS
    Br J Ophthalmol, 1990 Apr;74(4):215-9.
    PMID: 2186795
    The visual acuity, the difference in sensitivity of the two eyes to light (brightness ratio), and contrast sensitivity were assessed in 28 patients with chronic open angle glaucoma and compared with those of 41 normal controls of similar ages and visual acuity. The results obtained were related to the results of Tübingen visual field analysis in patients with glaucoma. Twenty-four of the 28 glaucoma patients (86%) had a significant disparity in brightness ratio between the two eyes. This was found to match the frequency of visual field loss. Moreover, there was a significant relationship between the interocular differences in brightness sense and the difference in the degree of visual field loss between the two eyes. Of the glaucoma patients 39% had sum contrast sensitivities outside the normal range for age-matched normal controls. No significant correlation was found between the interocular difference in brightness sense and the visual acuity or the interocular difference in sum contrast sensitivity. It is concluded that, in the presence of a normal visual acuity, the brightness ratio test warrants evaluation as a potential screening test for chronic open angle glaucoma.
    Matched MeSH terms: Photic Stimulation*
  11. Eng V, Lim A, Kwon S, Gan SR, Jamaluddin SA, Janssen SMJ, et al.
    Atten Percept Psychophys, 2017 May;79(4):1097-1106.
    PMID: 28229429 DOI: 10.3758/s13414-017-1295-8
    There are thought to be two forms of inhibition of return (IOR) depending on whether the oculomotor system is activated or suppressed. When saccades are allowed, output-based IOR is generated, whereas input-based IOR arises when saccades are prohibited. In a series of 4 experiments, we mixed or blocked compatible and incompatible trials with saccadic or manual responses to investigate whether cueing effects would follow the same pattern as those observed with more traditional peripheral onsets and central arrows. In all experiments, an uninformative cue was displayed, followed by a cue-back stimulus that was either red or green, indicating whether a compatible or incompatible response was required. The results showed that IOR was indeed observed for compatible responses in all tasks, whereas IOR was eliminated for incompatible trials-but only with saccadic responses. These findings indicate that the dissociation between input- and output-based forms of IOR depends on more than just oculomotor activation, providing further support for the existence of an inhibitory cueing effect that is distinct to the manual response modality.
    Matched MeSH terms: Photic Stimulation/methods*
  12. Rosli Y, Maddess T, Dawel A, James AC
    Clin Neurophysiol, 2009 Dec;120(12):2100-2108.
    PMID: 19846337 DOI: 10.1016/j.clinph.2009.09.006
    OBJECTIVE: To examine the feasibility of a multifocal visual evoked potential (mfVEP) binocularly, using a variant of the multifocal frequency-doubling (FD) pattern-electroretinogram (MFP).

    METHODS: Stimuli were presented in both monocular and dichoptic conditions at eight visual field locations/eye. The incommensurate stimulus frequencies ranged from 15.45 to 21.51 Hz. Five stimulus conditions differing in spatial frequency and orientation were examined for three viewing conditions. The resulting 15 stimulus conditions were examined in 16 normal subjects who repeated all conditions twice.

    RESULTS: Several significant independent effects were identified. Response amplitudes were reduced for dichoptic viewing (by 0.85 times, p<4 x 10(-11)); offset by increases in responses for between eye differences of one octave of spatial frequency: lower (1.15 times, 0.1 cpd); higher (1.29 times, 0.4 cpd), both p<1.8 x 10(-7). Crossed orientations produced significant effects upon response phase (p=0.023) but not amplitude (p=0.062).

    CONCLUSIONS: The results indicated that dichoptic evoked potentials using multifocal frequency-doubling illusion stimuli are practical. The use of crossed orientation, or differing spatial frequencies, in the two eyes reduced binocular interactions.

    SIGNIFICANCE: The results indicate a method wherein several spatial or temporal and frequencies per visual field region can be tested in reasonable time using a multifocal VEP using spatial frequency-doubling stimuli.

    Matched MeSH terms: Photic Stimulation/methods*
  13. Kalckert A, Perera AT, Ganesan Y, Tan E
    Exp Brain Res, 2019 Jul;237(7):1821-1832.
    PMID: 31079236 DOI: 10.1007/s00221-019-05539-6
    The rubber hand illusion (RHI) is a perceptual phenomenon in which participants experience ownership over a fake model hand through synchronous visuotactile stimulation. Several studies have shown that the illusion occurs only when both hands are in close proximity to each other. In the present study, we systematically examined the role of relative position (lateral, distal) and distance (13-75 cm) of the model hand (with respect to participants' real hand) on illusion experience across both lateral and distal positions. Furthermore, we also compared different facets of the subjective illusion experience; the experience of the model hand being part of one's body (i.e., ownership) and the perceptual fusion of vision and touch (i.e., referral of touch). In two experiments we observed indications for a stronger illusion experiences in distal compared to lateral positions of identical distances, indicating that the illusory effects may vary as a function of the relative position of the hand. Our results also showed that manipulations of distance differently modulated both facets of the illusion. While ownership was restricted to near distances, referral of touch sensations remained stable at farther distances. These results are interpreted in relation to variations in sensory weighting across different planes.
    Matched MeSH terms: Photic Stimulation/methods*
  14. Amir Kassim A, Rehman R, Price JM
    Acta Psychol (Amst), 2018 Apr;185:72-80.
    PMID: 29407247 DOI: 10.1016/j.actpsy.2018.01.012
    Previous research has shown that auditory recognition memory is poorer compared to visual and cross-modal (visual and auditory) recognition memory. The effect of repetition on memory has been robust in showing improved performance. It is not clear, however, how auditory recognition memory compares to visual and cross-modal recognition memory following repetition. Participants performed a recognition memory task, making old/new discriminations to new stimuli, stimuli repeated for the first time after 4-7 intervening items (R1), or repeated for the second time after 36-39 intervening items (R2). Depending on the condition, participants were either exposed to visual stimuli (2D line drawings), auditory stimuli (spoken words), or cross-modal stimuli (pairs of images and associated spoken words). Results showed that unlike participants in the visual and cross-modal conditions, participants in the auditory recognition did not show improvements in performance on R2 trials compared to R1 trials. These findings have implications for pedagogical techniques in education, as well as for interventions and exercises aimed at boosting memory performance.
    Matched MeSH terms: Photic Stimulation/methods*
  15. Chua KB, Chua IL, Chua IE, Chua KH
    PMID: 15689073
    A study was made of the oviposit behavior of gravid female Aedes mosquitos in man-made habitats under field conditions. The study showed that the gravid female Aedes mosquitos preferred containers with relatively easy access but not too open to external environmental influence. The dark surface of the containers served as the initial and long-range attractant to the breeding sites. Volatile chemicals generated by the decaying vegetation in the container may serve as a close-range attractant. Finally, the water quality and the quantity of 'food' derived from decaying vegetative matter in the water determined the amount of eggs deposited in each container. The study confirmed previous findings that each gravid female Aedes mosquito had the tendency to lay her eggs in more than one container. However, the results of the study suggests that under favorable conditions, each gravid female Aedes mosquito could be encouraged to lay all her eggs in a single breeding site.
    Matched MeSH terms: Photic Stimulation
  16. Swami V, Tovée MJ
    PLoS One, 2013;8(3):e57623.
    PMID: 23483919 DOI: 10.1371/journal.pone.0057623
    It has been suggested human female breast size may act as signal of fat reserves, which in turn indicates access to resources. Based on this perspective, two studies were conducted to test the hypothesis that men experiencing relative resource insecurity should perceive larger breast size as more physically attractive than men experiencing resource security. In Study 1, 266 men from three sites in Malaysia varying in relative socioeconomic status (high to low) rated a series of animated figures varying in breast size for physical attractiveness. Results showed that men from the low socioeconomic context rated larger breasts as more attractive than did men from the medium socioeconomic context, who in turn perceived larger breasts as attractive than men from a high socioeconomic context. Study 2 compared the breast size judgements of 66 hungry versus 58 satiated men within the same environmental context in Britain. Results showed that hungry men rated larger breasts as significantly more attractive than satiated men. Taken together, these studies provide evidence that resource security impacts upon men's attractiveness ratings based on women's breast size.
    Matched MeSH terms: Photic Stimulation
  17. Ahmad RF, Malik AS, Kamel N, Reza F, Amin HU, Hussain M
    Technol Health Care, 2017;25(3):471-485.
    PMID: 27935575 DOI: 10.3233/THC-161286
    BACKGROUND: Classification of the visual information from the brain activity data is a challenging task. Many studies reported in the literature are based on the brain activity patterns using either fMRI or EEG/MEG only. EEG and fMRI considered as two complementary neuroimaging modalities in terms of their temporal and spatial resolution to map the brain activity. For getting a high spatial and temporal resolution of the brain at the same time, simultaneous EEG-fMRI seems to be fruitful.

    METHODS: In this article, we propose a new method based on simultaneous EEG-fMRI data and machine learning approach to classify the visual brain activity patterns. We acquired EEG-fMRI data simultaneously on the ten healthy human participants by showing them visual stimuli. Data fusion approach is used to merge EEG and fMRI data. Machine learning classifier is used for the classification purposes.

    RESULTS: Results showed that superior classification performance has been achieved with simultaneous EEG-fMRI data as compared to the EEG and fMRI data standalone. This shows that multimodal approach improved the classification accuracy results as compared with other approaches reported in the literature.

    CONCLUSIONS: The proposed simultaneous EEG-fMRI approach for classifying the brain activity patterns can be helpful to predict or fully decode the brain activity patterns.

    Matched MeSH terms: Photic Stimulation
  18. Lenoble Q, Janssen SMJ, El Haj M
    Memory, 2019 02;27(2):231-238.
    PMID: 30021485 DOI: 10.1080/09658211.2018.1501068
    This study has developed an original approach to the relationship between eye movements and autobiographical memory, by investigating how maintained fixation could influence the characteristics of retrieved memories. We invited participants to retrieve autobiographical memories in two conditions: while fixating a cross at the centre of a screen and while freely exploring the screen. Memories retrieved during the maintained fixation condition were less detailed and contained less visual imagery than those retrieved during the free-gaze condition. Memories retrieved during the maintained fixation condition were retrieved slower and took less time to describe than those retrieved during the free-gaze condition. As for the characteristics of eye movements, analysis showed fewer and longer fixations as well as fewer saccades in the maintained fixation than in the free-gaze condition. Maintaining fixation is likely to tax cognitive resources that are necessary for the reconstruction of autobiographical memory. Our findings demonstrate how maintained fixation may result in a more effortful construction of autobiographical memory and memories with lower spatiotemporal specificity and poorer mental images.
    Matched MeSH terms: Photic Stimulation
  19. Lim A, Eng V, Janssen SMJ, Satel J
    Exp Brain Res, 2018 05;236(5):1369-1382.
    PMID: 29520444 DOI: 10.1007/s00221-018-5225-3
    Inhibition of return (IOR) refers to an increase in reaction times to targets that appeared at a previously cued location relative to an uncued location, often investigated using a spatial cueing paradigm. Despite numerous studies that have examined many aspects of IOR, the neurophysiological mechanisms underlying IOR are still in dispute. The objective of the current research is to investigate the plausible mechanisms by manipulating the cue and target types between central and peripheral stimuli in a traditional cue-target paradigm with saccadic responses to targets. In peripheral-cueing conditions, we observed inhibitory cueing effects across all cue-target onset asynchronies (CTOAs) with peripheral targets, but IOR was smaller and arose later with central targets. No inhibition was observed in central-cueing conditions at any CTOAs. Empirical data were simulated using a two-dimensional dynamic neural field model. Our results and simulations support previous work demonstrating that, at short CTOAs, behavioral inhibition is only observed with repeated stimulation-an effect of sensory adaptation. With longer CTOAs, IOR is observed regardless of target type when peripheral cueing is used. Our findings suggest that behaviorally exhibited inhibitory cueing effects can be attributed to multiple mechanisms, including both attenuation of visual stimulation and local inhibition in the superior colliculus.
    Matched MeSH terms: Photic Stimulation
  20. Ismail SA, Sharanjeet-Kaur, Mutalib HA, Ngah NF
    J Optom, 2015 Oct-Dec;8(4):266-72.
    PMID: 26025808 DOI: 10.1016/j.optom.2015.04.001
    PURPOSE: To determine the influence of age and gender on macular sensitivity to light in healthy subjects of 4 age groups using the MP-1 microperimeter.
    METHODS: A prospective study was carried out on 50 healthy subjects (age range: 18-60 years) divided into 4 age groups; 18-30 years, 31-40 years, 41-50 years and 51-60 years. Full-threshold microperimetry of the central 10° of retina was performed utilizing 32 points with the MP-1. Macula area was divided into four quadrants, which were superior nasal (SN), inferior nasal (IN), inferior temporal (IT) and superior temporal (ST).
    RESULTS: Total mean sensitivity at 10° for age groups 18-30 years, 31-40 years, 41-50 years and 51-60 years were 19.46 ± 0.30, 19.40 ± 0.39, 19.47 ± 0.35 and 18.73 ± 0.75 (dB), respectively. There was a significant difference in total mean retinal sensitivity at 10° and at the four quadrants with age but not for gender. The retinal sensitivity was highest in the IT quadrant and lowest in the SN quadrant for all age groups. The linear regression analysis revealed that there was a 0.019 dB, 0.016 dB, 0.022 dB, 0.029 dB and 0.029 dB per year age-related decline in mean macular sensitivity within the central 10° diameter in the SN, IN, IT and ST quadrants respectively.
    CONCLUSION: Among normal healthy subjects, there was a linear decline in retinal light sensitivity with increasing age with the highest reduction in the superior nasal quadrant and lowest in the inferior temporal quadrant.
    Matched MeSH terms: Photic Stimulation/methods
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