Eye Movements of Younger and Older Drivers Professor: Liu Student: Ruby

Objective The study experiment younger and older people’s eye movements in task-directed and task-undirected visual search. Recorded the search times, number of fixations, and fixation durations from one digit to the next.

References Older people have poorer visual tracking skills because their peripheral vision was decreased. (Whiteside,1974; Bono et al., 1996; Kanayama et al., 1994; Kline, 1994; Olincy, Ross, Young, & Freedman, 1997). Using the UFOV discovered that crashes were related to older drivers’ age, visual acuity, or mental status. (Ball, Beard, Roenker, Miller, & Griggs, 1988; Ball & Owsley, 1991; Ball et al., 1993; Ball & Rebok, 1994)

References The inattention was a more reliable factor of crashes than visual functions or eye health. (Ball et al., 1993) Older participants’ mean search times were longer than younger participants, therefore older people have a less ability to search. (Schieber, 1989)

Method Participants: –Older group: 3 women and 2 men. age from 20 to 30 years old. median driving experience: 37 years. –Younger group: 3 women and 2 men. age from 62 to 80 years old. median driving experience: 8 years. The eyesight required in 6/9.

Method Stimulus photos and equipments –Four images were chosen which included pedestrians, oncoming, passing, and intersecting cars. –Two images which used in Schieber’s research, one had numeric in the image and the other did not have. –386 PC and 14-inch monitor. –ASL 210 eye tracking system and Spectra- Sensors which collect the data.

The CVRT had numerical in the image

Method Procedure –Training section: participant was presented with a sample image. –The numerical overlay image was always shown second and fifth in the series. – As each number was found, the participant pressed a button. –A scanning time of 10 s was allocated per image.

Results & Discussion Numerical Overlay Pictures –Search time The mean search time to complete the task for the older participants was significantly higher than younger participants. t = 2.33, p =.01.

Results & Discussion The longest search times of the older participants were significantly longer than younger participants t(29) = 4.7, p <.001.

Results & Discussion Fixation –The number of fixations showed significantly more fixations for the older group, F(1, 8) = 16.85, p =.003. The longer total search time for the older participants was caused by an increase in the number of fixations rather than an increase in their duration. –There was a significant drop in saccade amplitude from the first presentation (mean = 6.7°) to the second one (mean = 6.1°), F(1, 8) = 11.04, p =.01.

Results & Discussion Fixation –Search duration correlated negatively with the mean saccade amplitude, r = –.45, p =.01. Participants were having a difficult search, which their saccade amplitudes tended to be shorter.

Results & Discussion CVRT. (the number reached (out of 14) in 10 s. –The number of fixations related with the participant’s test scores, r = –.73, p =.02. –Lower relation between saccadic amplitude and CVRT, r =.62, p =.06. –A small negative correlation between CVRT test score and search time.

Results & Discussion Comparing Visual Search of the Numerical Overlay and Traffic Scene Images –There was a high relation between the images, r = 0.79, p =.01. Saccadic amplitude is also a consistent mark of a person’s visual search behavior. –Rayner & Pollatsek in 1992 discovered that the thickness of information on the image which influence strongly on saccadic extent.

Results & Discussion Traffic Scene Images –The authors divided the four traffic scene images into areas of interest (AOI) appropriate for driver attention. Mean dwell time outside the AOIs was 20%–34%. There was no significant effect of age, F(1, 6) = 2.39, p =.17.

Results & Discussion There were significant interactions between age group and AOI for: –Image 3, F(3, 18) = 10.5, p <.001. – Image 4, F(2, 16) = 4.01, p =.04. The older participants in both of images tended to ignore some AOIs while focusing for an very long time on a subset of the AOIs.

Results & Discussion Concentration ratio –The degree to which certain areas are fixated on more than expected. –Older people really concentrate their fixations on a more limited number of AOIs. Concentration ratio : Σ|Fi – Ai|.

Results & Discussion Older participants showed increased concentration in a smaller number of AOIs. The mean concentration ratio of the old group was significantly higher than young group, F(1, 6) = 18.5, p =.005. There was significant interaction between image and age, F(3, 18) = 6.1, p =.005. –Only three out of the four images reflect difference in the concentration ratio.

Results & Discussion Two possible visual search models could explain the differences between the older and younger participants. –Older participants confine the number of AOIs that they scan and dwell for longer periods of time. –Older participants’ fixations jump one AOI to the next, and the confine number of AOIs on which they fixate reflects saccadic movements to AOIs.

Results & Discussion stability ratio: Px|y(x|y)/Px(x). – If the ratio is close to 1, then the participant’s fixation pattern is fairly random or uniform across the whole image. –The participant’s fixation in a particular AOI is independent of the previous fixation. –As the ratio gets higher, the visual search becomes stable.

Results & Discussion The younger participants were stable than the older participants, F(1, 6) = 13.02, p =.01. The main effect of image and the interaction between image, F(3, 18) =.69, p =.57 and age were not significant, and F(3, 18) =.39, p =.76.

Conclusion Older persons need longer visual search times than younger persons to get the same information. Older people’s visual search behavior is characterized: (a) Large variability in the data from the older group. (b) Occasional lapses that occurs in searching difficulty.

Conclusion The older participants’ eye movements were characterized by shorter saccades and increased numbers of fixations caused by: (a) A poor visual search process with ineffective use of the peripheral field (b) A failure to get amounts of information from areas that were before fixated on.

Conclusion The older participants focused on a smaller subset of the areas of interest within the images. The younger participants distributed their attention more equal different parts of the scene. People tend to have the same general type of saccadic movement for different types of tasks. Saccadic eye movements may be a stable indication of individual differences.