Biomedical subjects

M Adjouadi

Publications and source records attributed to M Adjouadi.

6 recordsLinked to original sources

PubMed2000

Relating induced changes in EEG signals to orientation of visual stimuli using the ESI-256 machine.

The focus of this study is to investigate the relations that exist between changes in the orientation of simple visual stimuli displayed to a subject and the induced changes in brain activity recorded as EEG signals. These signals are recorded using the Electric Source Imaging with 256 electrodes (ESI-256). The 256-channel EEG signals of four subjects were measured monopolarly. Each subject was stimulated visually for approximately 7.5 minutes. The stimuli consisted of a series of 300 images depicting four basic orientations of a simple graphical element: a white bar on a black background, with each one of the four orientations (horizontal, vertical, +45 degrees and -45 degrees) shown a total of 75 times in a random order. The notion of missing information under certain orientations is not addressed at this juncture. The EEG signals produced by each subject were recorded in a continuous mode using a sampling rate of 1 kHz. Pre-processing of the raw EEG data obtained consisted of epoching, exclusion of faulty electrodes, and reduction of electro-oculogram (EOG) noise due to eye blinks. Topographical maps displaying brain activities and their individual electrode recordings are used as two different means for assessing these changes. It is important to note that the simplicity of the visual stimuli was considered in view of the massive data collected for interpretation. Our goal is to observe and determine new measures that would allow for the quantification and interpretation of such EEG brain activities. Such findings might prove useful for the later use of more complex stimuli and the potential development of size and orientation independent algorithms in image processing.

Brain Mapping↗

PubMed2000

Decreased 3D-sound spatialization accuracy caused by speech bandwidth limitation over commodity audio components.

This paper studies the accuracy achievable in spatialized speech signals due to their limited bandwidth, in systems based on generic Head-Related Transfer Functions (HRTFs). The accuracy in the perception of sounds spatialized through HRTFs to emulate nine sound locations around the listener, at 0 elevation, are investigated. The tests contrast the localization accuracy for a speech segment and that for broadband noise, as perceived by two independent groups of 10 normal-hearing volunteers each. The sound localization perceived and reported by each subject is compared to the HRTF-emulated location, to define a localization error, in each case. The results are analyzed through a repeated measures, mixed-factorial design Analysis of Variance (ANOVA). The emulated source locations and the type of sounds are the independent variables, and the average perceived localization error for each case, the dependent variable. Since the spectrum of speech signals drive only sections of the complete HRTF frequency response for each location, the initial expectation is that they benefit less from the spectral-shaping process implemented by the HRTFs, thus resulting in a lower spatialization efficiency than the one for a full-spectrum noise signal. We study the measurement of these effects when 3D-sounds are delivered over commodity audio components, because of their widespread use in practical systems.

Adult↗

PubMed1997

A directional clustering technique for random data classification.

This paper introduces a new clustering technique for random data classification based on an enhanced version of the Voronoi diagram. This technique is optimized to deal in the best way possible with data distributions which in their spatial representations experience overlap. A mathematical framework is given in view of this enhanced analysis and provides insight to key issues involving (a) the use of a correction process to complement the traditional Voronoi diagram and (b) the introduction of directional vectors in Gaussian and elliptical data distributions for enhanced data clustering. The computational requirements of the proposed approach are provided, and the computer results involving both randomly generated and real-world data prove the soundness of this clustering technique.

Data Interpretation, Statistical↗

PubMed1995

An augmented computer vision approach for enhanced image understanding.

This paper addresses the design concept of a spatially and spectrally augmented computer vision approach toward enhanced image analysis and understanding. The concept of spatially augmented computer vision refers to the inclusion of the stereo disparity measure (1/2-D) along with the two-dimensional (2-D) spatial coordinates of the images, together yielding the augmented (2 1/2-D) representation. The concept of spectrally augmented computer vision refers to the implementation of the multiresolution concept of the wavelet theory to analyze and assess in detail the local properties of the 2-D images. The principal objective in applying this augmented, and more revealing, computer vision approach is to provide the added dimension in spatial and spectral resolutions for the enhanced understanding of images. To this end, imaging techniques are developed to exploit, in an optimal fashion, the information acquired by the camera system to yield useful descriptions of the viewed scenes. Experimental results are provided in support of this research direction.

Image Processing, Computer-Assisted↗

PubMed1992

A man-machine vision interface for sensing the environment.

This study describes a computer vision approach for sensing the environment with the intent of helping people with a visual impairment. The principal goal in applying computer vision is to exploit, in an optimal fashion, the information acquired by the camera(s) to yield useful descriptions of the viewed environment. The objective is to seek efficient and reliable guidance cues in order to improve the mobility needs of individuals with a visual impairment. In this research direction, the following problems are identified and addressed: 1) the vision system design; 2) establishment of the mapping principles between the two-dimensional (2-D) camera images and the three-dimensional (3-D) real world; 3) development of appropriate imaging techniques for the interpretation of the 2-D images; and, 4) establishment of a communication link between the vision system and the user. The soundness of this research direction is assessed by means of a theoretical framework and experimental evaluations.

Algorithms↗

PubMedDate not supplied

A practical EMG-based human-computer interface for users with motor disabilities.

In line with the mission of the Assistive Technology Act of 1998 (ATA), this study proposes an integrated assistive real-time system which "affirms that technology is a valuable tool that can be used to improve the lives of people with disabilities." An assistive technology device is defined by the ATA as "any item, piece of equipment, or product system, whether acquired commercially, modified, or customized, that is used to increase, maintain, or improve the functional capabilities of individuals with disabilities." The purpose of this study is to design and develop an alternate input device that can be used even by individuals with severe motor disabilities. This real-time system design utilizes electromyographic (EMG) biosignals from cranial muscles and electroencephalographic (EEG) biosignals from the cerebrum's occipital lobe, which are transformed into controls for two-dimensional (2-D) cursor movement, the left-click (Enter) command, and an ON/OFF switch for the cursor-control functions. This HCI system classifies biosignals into "mouse" functions by applying amplitude thresholds and performing power spectral density (PSD) estimations on discrete windows of data. Spectral power summations are aggregated over several frequency bands between 8 and 500 Hz and then compared to produce the correct classification. The result is an affordable DSP-based system that, when combined with an on-screen keyboard, enables the user to fully operate a computer without using any extremities.

Biofeedback, Psychology↗