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Jeff C Rabin, Timothy Bradshaw, Alicia Chacon, Shawn Johnston, Dennis Yu; Hands-Free Phone Communication Impairs Low Contrast Color and Luminance Target Recognition. Invest. Ophthalmol. Vis. Sci. 2014;55(13):6240.
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Distraction from cell-phone use while driving has been linked to auto accidents, injuries and fatalities. Despite widespread banning of hand-held phones, hands-free systems are ubiquitous and standard in newer vehicles. Nevertheless, the impact of hands-free communication on visual performance and safety remain unclear. Our purpose was to determine whether hands-free communication impairs color and luminance contrast sensitivity (CS) and response time (RT).
A Netbook computer (Innova Systems, Inc.) was used to measure luminance CS for recognition of large (20/700) and small (20/50) grey letters on a white background and cone-specific color CS (red, green, violet 20/400 letters on grey background visible only to L,M or S cones). Single letters appeared in the center of the display and the subject used a mouse to select each letter seen from an adjacent matching display. A response-driven staircase measured the lowest visible contrast (CS), mean & threshold RT for each of the five CS tests. Sixteen color vision normal (CVN) and 12 color vision deficient (CVD) subjects were tested binocularly in a dark room at 3 ft. under two conditions: Verbal Communication (VC) in which each subject responded verbally (“hands free”) to a simulated phone call broadcast on a Bluetooth device immediately above the subject. The VC lasted for the duration of each CS test and required that the subject answer scripted questions involving cognition and decision making. Each subject also completed all CS tests with no VC (NVC) with test order counterbalanced across subjects.
Compared to NVC, there was a significant increase in average RT (p<0.00001) and threshold RT (p<0.002) with VC on all CS tests (mean increase = 270 ms; 52% of threshold RTs and 27% of average RTs increased ≥ 500 ms with VC). There was no decrease in large letter CS (p>0.22) but small letter CS decreased with VC (p<0.05). In CVNs color CS decreased slightly with VC (p<0.05), and green and red cone CVDs showed decreased green CS with VC (p<0.05), while decreased red cone CS approached significance (p=0.07).
Hands-free phone communication impairs sensitivity and increases response time for recognition of low contrast luminance and color targets. Despite widespread legalized use of hands-free communication during driving, low contrast target recognition can be delayed and impaired posing a formidable threat to safety.
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