the study of what is known as subjective contours or illusory contours Later Coren and A. Ralph Hakstian developed methods for screening vision and hearing without the use of technical equipment, using behaviorally validated questionnaires. These allow group or survey testing for sensory deficits specifically for color blindness, color discrimination ability, visual acuity, binocular vision and stereopsis and hearing sensitivity or absolute threshold of hearing. These tests have been widely disseminated and can be found reprinted in various psychological and sensory textbooks. Handedness Coren worked on left-handedness and its causes and consequences, with his co-researchers, Diane F. Halpern, Clare Porac, and Alan Searleman. Specifically his research led him to believe that left-handedness could be a marker for various psychological and physical problems. The media became interested in this work when findings began to emerge indicating that left-handedness was often associated with difficult or stressful births. Research showing that left-handers were much more susceptible to accident-related injuries because the constructed world and most machinery and tools are designed for the safety and convenience of right-handers evoked a great deal of interest and press coverage. However the work that caused the largest stir and the most controversy was a series of studies in collaboration with Diane F. Halpern which showed that left-handers have shorter life spans, often dying younger because of accidents or problems associated with a compromised immune system (possibly a long-term consequence of birth stress related trauma). Although originally the source of much controversy, with confirming data coming from a number of other laboratories, these conclusions have become well enough accepted to appear in basic psychological textbooks. The discovery of a possible genetic basis of left-handedness suggests that there may be two types of left-handers, natural left-handers and a separate group who arrive at their left-handedness because of birth stress and are more susceptible to immune system related problems. Coren has suggested that in addition to genetics and birth stress other mechanisms might also contribute to the appearance of left-handedness, such as hormonal factors as in the Geschwind–Galaburda hypothesis. Sleep Coren 's research into sleep deprivation suggests that this is contributing to accidents, psychological disturbances, and increased susceptibility to illness. This line of reasoning eventually led to the series of studies which demonstrated that simply losing one hour of sleep due to the shift to daylight saving time can cause an increase in traffic accidents and other accident related fatalities