Temporal visual processing loss in ageing and its contribution to altered driving behaviour

2.1.1 Hypothesis

Our principle objective is to test whether reduced visual processing time measured by the Vernier masking task is related to poorer on-road driving performances or increased driving restrictions. Our secondary objective is to explore other potential determinant of driving behaviours from computed visual processing or cognitive function tasks.

2.1.2 Methods

This study coupled data collected from common participants in the GARAge study, (a cohort study under way, measuring cognitive predictors of motor vehicle collision and driving cessation) and a study in psychophysics on ageing and metabolism. In spring 2013, 52 older adults (≥70 years) were recruited, using the same method as the one described for the derivation and validation studies for MedDrive.

Participants underwent an on-road driving evaluation with a driving instructor who was blinded to their health condition or their psychophysical performance. A researcher collected information on driving behaviour and driving restrictions during a two-hour interview prior to psychophysical measurements. Self-restriction was evaluated using the same questionnaire as the one described for MedDrive’s validation study. Participants were then requested to attend the lab twice for test sessions lasting 2 ½ –3 hours each.

During those two sessions, a researcher, blind to the results from the on-road evaluation, tested:

visual acuity (Landolt C, FrACT version 3.7l) contrast sensitivity (Gabor patch)

visual backward masking (vernier task) motion direction sensitivity

orientation discrimination sensitivity biological motion

visual search (16 objects) the Simon effect

simple response time

executive functions (Wisconsin Card Sorting Test) verbal fluency

working memory (digital forward and backward task).

The vernier task consisted of presenting stimuli from a distance of five meters in a dimly illuminated room. A pixel of the screen comprised about 18 arc seconds at this distance. The stimuli were white (100 cd/m2) on a black background. In a first step, we presented vernier stimuli that consisted of two vertical bars of 10 arc minutes length that were offset in the horizontal direction. In each trial, the vernier offset direction was chosen randomly. Participants indicated the offset direction of the lower

signal. For each observer, we determined the individual vernier duration (VD) to reach 75% correct responses, using a staircase procedure. In the second step, we used a vernier offset size of 1.15 arc minutes for all observers and individual VD as defined in the first step. The vernier was followed by a variable inter-stimulus interval (ISI), that is, a blank screen, and then a grating was displayed for 300 millisecond.

The grating consisted of either 5 or 25 verniers, without offset, of the same length as the target vernier. The 5 element grating leads to stronger masking than the 25 element grating even though the 5 element grating is contained in the 25 element grating.

This difference in masking strength indicates that a substantial part of the masking power is not of retinal origin because retinal processing is mainly determined by the sheer amount of light; for example, the number of grating elements presented. In addition, we used both the 5 and 25 element gratings to cover the different ranges of sensitivity of patients and controls. The elderly showed strong deficits with the 25 elements grating, whereas controls performed in the ceiling regime. In the current study, we again expect ceiling performance with the 25 elements grating in the elderly populations, but expect the 5 element grating to be more sensitive to reveal deficits.

The horizontal distance between grating elements was about 3.33 arc minutes. We varied the ISI adaptively using a staircase procedure. We assessed the ISI target that yields a performance level of 75% correct responses. The starting value of the SOA was 200 milliseconds. Conditions were presented in two blocks of 80 trials.

Amendments to protocol CE 157/2011 and CE 384/2011 were accepted in May 2013, to obtain participants’ consent to share data between both studies for the purpose of this study. All participants gave their informed written consent prior to their inclusion.

Both studies were performed in accordance with the ethical standards of the 2008 amended Declaration of Helsinki (Seoul). field ≥ 120 °; all other participants had a visual field ≥ 140°. Two participants had a visual binocular acuity of less than 0.6 decimal and the average contrast threshold was Gastric reflux or acidity 11.5% (6)

Chondrosulfites 11.5% (6) Cardio-vascular disorder 7.7% (4)

Other condition 9.6% (5)

Table 2: Vision and medical history in studied

2. – Analysed data yet to be published

participants did not require any medical visit during the previous twelve months other than for a check-up. Four patients were under medication that is known to affect fitness for driving (antihistamines, benzodiazepines, anti-epileptics). Description of eye deficits and medical history are provided in Table 2.

In addition to driving a car regularly during the past two years, 30 participants (57.7%) also rode a bicycle, two drove a farm vehicle and two a motorbike. Their self-reported average weekly driving distance was 247 kilometres (SD=138), ranging from 50 to 550 kilometres. During the past two years, 20 drivers (38.5%) reported having been involved in an accident that caused material damage. In three of these accidents, they were liable for damage occasioned to someone else’s property. Forty-four participants (84.6%) lived closer than 2 kilometres to the closest grocery store;

and 25 (48.1%) lived less than five minutes’ walking distance to the closest public transport.

We did not observe any linear association between on-road driving performance and vernier duration (R²=0.001, p=0.808), SOA25 (R2<0.001, p=0.838) or SOA5 (R²=0.030, p=0.215). Comparison between excellent and satisfactory drivers is provided in Table 3. The area under the receiver-operating curve was of 0.518 (CI95% 0.352 to 0.683) for SOA25 and of 0.599 (CI95% 0.436 to 0.761) for SOA5, suggesting SOAs do not contribute significantly in distinguishing excellent drivers from other drivers and that increased visual processing does not necessarily affect on-road driving behaviour.

Table 3: Vernier masking and driving behaviour. Δ Means = difference between means, R² = coefficient of determination, SOA = stimuli onset asynchrony

Thirty-seven drivers (71.2%) reported finding it useful to apply restrictions to their driving. This most often concerned driving in the fog (28 drivers), in dense traffic (15 drivers) or in the dark (14 drivers). Only one driver reported it as “slightly useful” to not drive on highways and another as “useful” not to drive alone. The driving restriction score ranged from 0 to 6 (Figure 1), 20 being the maximum possible score for someone finding it indispensable to apply all forms of restrictions.

  Drivers  with  no  

restriction   Difference  for  drivers  with  driving  restrictions  

  Crude     Adjusted  for  age  

  [CI95%|   Δ  Means  [CI95%|   R²     Δ  Means   P-­‐value  

Vernier  duration  (ms)   63  [14  to  112]   34.5  [-­‐24  to  93]   R²=0.028     27.3   P=0.332   SOA25  (ms)   73  [25  to  121]   45.3  [-­‐12  to  102]   R²=0.049     44.1   P=0.131   SOA5  (ms)   150  [105  to  195]   76.8  [23  to  131]   R²=0.141     76.6   P=0.007  

Table 4: Vernier masking and driving self-restriction. Δ Means = difference between means, R² = coefficient of determination, SOA = stimuli onset asynchrony

We found a significant linear correlation between driving restriction score and SOA5 (R²=0.122, p=0.012). This association was independent of age (p=0.012) or of age and eye disorder (p=0.013). Even if a similar trend was observed for SOA25 (R²=0.041, p=0.151), and in a lesser degree for vernier duration (R²=0.028, p=0.238), these remained non-significant. SOA25 and SOA5 could significantly discriminate senior drivers who adopted driving restrictions from those who did not (Table 4). The

area under the receiver-operating curve was of 0.635 (CI95% 0.471 to 0.799) for SOA25 and of 0.744 (CI95% 0.595 to 0.893) for SOA5.

The magnitude of the association between SOA5 and driving restriction score remained similar, independent of the vernier duration. Those with a vernier duration ≤ 100 milliseconds revealed a decreased SOA5 of 17.3 milliseconds for each point on the driving restriction score (CI95% 1.3 to 33.2, p=0.035) and those with vernier duration > 100 milliseconds revealed a decreased SOA5 by 20.1 milliseconds (CI95%

-11.3 to 51.4, p=0.190).

Education level and visual processing from the useful field of view (UFOV) were the only two measurements associated with on-road driving performance (Table 5).

Those with a higher education level revealed worse driving performances. Together, UFOV and education level were able to explain 30.5% of the variance of the on-road

Figure 1: Vernier masking task and driving behaviour. Vernier duration (A), SOA5 (B), and SOA25 (C) association with driving performance (on-road evaluation) and driving restrictions were evaluated for 52 senior drivers.

Intervals correspond to 95%CI. R2 = coefficient of determination; SOA = stimuli onset asynchrony.  

2. – Analysed data yet to be published

driving score. However, for education, an opposite non-significant trend (R2=0.002, p=0.344) was observed when analysing all the 417 drivers we tested. Furthermore, the association with the UFOV was not as important on this larger sample (R2=0.014, p=0.016). The predictive power of education and the UFOV is, therefore, probably exaggerated in the smaller sample and must be interpreted with care. There, the association between education level and SOA5 was nevertheless weak and non-significant (R2=0.037, p=0.173). This could be important as education was also associated with the driving restriction score – those with higher education levels reporting more restrictions.

Educations (years of schooling) 0.146 0.005 0.090 0.030

Optical tests

Visual acuity (FrACT arc minutes) 0.043 0.138 0.002 0.748

Contrast sensitivity threshold (candela per m²) 0.004 0.643 0.031 0.210 Neuropsychological tasks

Mental flexibility (Perseverative errors WCST [%]) 0.023 0.295 <0.001 0.934

Working memory (Digit backwards [n°]) 0.005 0.630 0.020 0.314

Verbal Fluency ([animals + fruits-veg.] /2 [n°/min]) 0.071 0.056 0.002 0.757 Computed tasks

Simple response time (ms) 0.021 0.303 0.012 0.434

Visual search (RT [ms]) <0.001 0.837 0.034 0.191

Motion direction threshold (%) 0.007 0.547 0.009 0.504

Orientation discrimination threshold 0.051 0.108 0.003 0.702

Biological motion index (%) <0.001 0.966 <0.001 0.843

Incongruency (Simon’s effect Δt [ms]) 0.017 0.358 0.045 0.131

Useful field of view

Visual processing 0.222 0.001 0.077 0.059

Divided attention 0.007 0.579 0.032 0.231

Selective attention 0.080 0.053 0.010 0.513

Visual processing (Vernier’s Task)

Table 5: Associations of stimuli-onset asynchrony with other measurements of vision, cortical processing or cognitive functions (n=52) * significance level for linear correlation.

FrACT = Freiburg Visual Acuity and Contrast test, R2 = coefficient of determination, SOA 5 = asynchrony measuring feature inheritance, SOA 25 = stimulus-onset-asynchrony measuring shine through.

2.1.4 Contribution and acknowledgments

Paul Vaucher recruited participants, collected data on driving performance, planned the analysis and analysed data. Michael Herzog and Daniela Herzig from the Laboratory of Psychophysics, The Brain Mind Institute, EPFL, supervised Paul Vaucher in writing the methods and results section for this study. Daniela Herzig collected data, interpreted results and co-wrote the article draft.

2.2 Ability of goal-oriented control to compensate for reduced inhibition