Thesis - Instituto de Telecomunicações

30 CHAPTER 2. STATE OF THE ARTeye activities. In [180] an approach based on Visual Evoked Potential (VEP), where imagesare shown to 102 subjects, obtained an error near 10%.Advantages and Disadvantages The case for an EEG biometric system is hard todefend. Recent studies are more concerned with the answer to the research question thanto propose a viable system.The EEG acquisition is one of the most intrusive techniques described in this chapter.This technique is time consuming and with several hygiene concerns. Conventional EEG acquisitionneeds the application of special conductive gels to improve the conductive contactwith the skull skin. Some recent improved designs for EEG signal acquisition systems havebeen developed, for reduced and specific locations in the head. The overall design has improvedand usability has increased in the sense that they are now easier to place [122, 150].Nevertheless the usage of such a system is, as yet, far from acceptance for regular use.2.3.9 Related TechniquesThere are additional research works related to user behavior. While these cannot be consideredas biometric techniques, they have some interesting characteristics related to thisclass of biometric applications.In [31], a user identification system is designed based on a page of handwritten textwriting style. In [208], the user is identified by the graphical characteristics of his cursivehandwritten text. The authors use an image of a page of handwritten text and extractfeatures from the several lines and words. This new approach was used to create the traitcalled write print [144]. This is a content analysis idea that tries to classify users in diversegroups or even to verify their identity via their textual writing style.Graphical passwords [49, 120, 230] have been proposed as a more secure system thannormal textual passwords. The user sketches a small picture using an electronic pen (thesystem is proposed for use in PDAs with graphical input via a stylus). The authors claimthat secret drawing is more memorable and presents more diversity than textual passwords.