The effect of reduced field of view on the safety of crossing decisions

Abstract

Purpose : My lab has previously shown that pedestrians with a combined Visual Field (VF) and acuity loss make significantly more unsafe crossing decisions compared to pedestrians with only an acuity loss. Based on this finding, this study aimed to further explore how the safety of crossing decisions changed as a function of VF size.

Methods : 31 young (mean age: 25.2 years) and 19 older subjects (mean age: 73.8 years) with normal vision made crossing decisions about whether or not they thought it was safe to cross a one-way street with one lane of traffic under three different VF size viewing conditions: (1) Full VF; (2) 20⁰ diameter; and (3) 10⁰ diameter. Crossing decisions for each VF size were made for a range of vehicular gap times. The percentage of unsafe decisions (%Unsafe) was calculated for each subject for each VF size by computing the number of times a subject deemed it was safe to cross when the measured gap time for that trial was shorter than the subject’s measured crossing time. A linear mixed model with repeated measures for subject was used to determine if the %Unsafe decisions changed as a function of age and VF size.

Results : Older subjects made significantly more %Unsafe decisions compared to the young subjects (p=0.0004). The effect of VF size on the %Unsafe decisions was affected by age (p<0.0001). Specifically, for the young subjects, there was a trend that more %Unsafe decisions were made as the VF size decreased going from Full to 10⁰, but this reduction was not significant (p=0.67). There was a significant increase in the %Unsafe decisions for the young subjects going from 20⁰ to 10⁰ (p<0.0001). Surprisingly, young subjects made significantly more %Unsafe decisions under the Full VF condition compared to only having a 20⁰ VF size (p=0.001). For the older subjects, the %Unsafe decisions increased significantly when the VF size reduced from Full to 20⁰ (p<0.0001) and from Full to 10⁰ (p<0.0001). No significant difference in %Unsafe decisions were found between 20⁰ and 10⁰ (p=0.54) for the older subjects.

Conclusions : Our data suggests that reductions in the VF size to the level of legal blindness (20⁰ diameter) increased the level of difficulty of making safe crossing decisions for older pedestrians but not for younger pedestrians. A further reduction in VF size to 10⁰ diameter resulted in increased difficulty in decision-making for the young but not for the older pedestrians.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.