Custom software for the Attended Field of View test was made using the Experiment Builder (SR Research®, Toronto, Canada). A 19in. LG monitor connected to a 2.4GHz Intel Core PC was used to display the stimuli. The participants were seated 50cm from the screen with their eyes aligned to the center of the screen. A standard keyboard and mouse were used to respond to the stimuli.

The AFOV test was designed following Coeckelbergh et al.15 and involved binocular detection and localization of a white target (Landolt C) that subtended 1.1° at 50cm with a gap of 0.2°. The Landolt C had to be detected in an array of 24 white rings. The rings were positioned on a grid along eight radii (oriented at 0, 45, 90, 135, 180, 225, 270, and 315°) and at three eccentricities (4, 8, and 12° from the center of the screen). The target and the distracter rings appeared on a gray background giving 50% contrast. One white ring also appeared in the central location, although the target never appeared at this location. The target and the other elements appeared simultaneously in the display – Fig. 1. The target (Landolt C), oriented in one of the four possible directions (up, down, left, right), was displayed at 9 of the 24 possible locations (3 locations at each eccentricity) presented in random order, except that the location of the target was never at the same location as in the previous trial. The nine locations were positioned on the 45 and 135 meridia. Participants were not informed that only nine locations were tested. The time taken to perform the test would have been considerably longer if all the available 24 locations were tested, potentially making fatigue an issue. Upon debriefing after the experiments, the participants responded that they were not aware that only some locations were tested.

Figure 1.

Representation of AFOV stimuli: standard AFOV (top left), standard AFOV with pop out distracter (top right), dual AFOV (bottom left), dual AFOV with pop out distracter (bottom right).

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The experiment started with a central fixation cross being displayed for one second. Following this, the display containing the target at one of the nine locations and the other white circles (distracters) appeared (see Fig. 1). The initial presentation time was set at 350ms. Following this, a mask (a combination of black, white and gray squares) appeared for 800ms. The purpose of the mask was to eliminate any afterimages of the target and distracters. After the mask, the response screen appeared and the participants had to move the mouse and click at the location where the target was observed. If the target was not observed, the participants were asked to guess. In the next screen, the orientation of the target was indicated by pressing the up, down, left or right arrow key on the keyboard. Following this, the fixation cross appeared at the central location and the procedure was repeated for the next trial. Those individuals who had difficulty with the mouse and keyboard were asked to point to the location and verbally report the orientation. The experimenter entered these responses using the mouse and keyboard for every trial. An independent staircase for the presentation time was run at each of the nine target locations. The presentation time was increased if localization of the target was incorrect and decreased if it was correct, in a weighted up-down manner (0.2 log unit up and 0.1 log unit down), such that the percentage of increase was higher than the decrease, resulting in a 67% correct threshold. Forty trials were presented at each location and in all cases more than 8 reversals were obtained. The average of the response reversals for each eccentricity, excluding the highest and lowest reversal values, was taken as the measure of time to locate the target. Although the orientation of the Landolt C was to be judged, this judgment did not affect staircase presentation time. This first experiment will be referred to as the “standard AFOV” (Fig. 1 – top left panel).

In the second experiment, the effect of a single pop out distracter on AFOV performance was investigated. The experimental task remained the same, but in this case, one of the white rings was replaced with a red ring (pop out distracter). The location of the red pop out distracter varied with every trial randomly, occupying one of 23 available positions. The participants were instructed to ignore the red ring and still search for the target (Landolt C) (Fig. 1 – top right panel). The location of the target and the orientation of the “C” were identified as described in the first experiment. Experiment two will be referred to as “standard AFOV with pop out distracter”.

In the third experiment the AFOV test was modified to create a dual task situation. The central target was replaced with an arrow oriented in one of four directions (up, down, left or right). The experiment started with the display of a central fixation cross lasting for one second. After this the stimulus containing the target (Landolt C) at one of the nine locations and the distracters (other white circles) appeared along with the central arrow oriented in one of the four directions (Fig. 1 – bottom left panel). The position and orientation of the Landolt C and the direction of the arrow were randomized independently. This display was followed by a mask lasting for 800ms, as before. In this case, the participants were required to first report the direction of the central arrow (using the arrow keys on the keyboard) and then indicate the location of the target. A response regarding the orientation of the Landolt C was not required in this case. This was done to avoid confusion between the orientation of the central target and the direction of the Landolt C. As in the standard AFOV, 9 locations were tested (3 at each eccentricity). Participants were not informed of the fact that some locations were not tested. Forty trials were presented at each location and in all cases more than 8 reversals were obtained. In cases where the response for the direction of the central arrow was wrong, the trial was put back into the sequence of the staircase for that location. Details regarding the staircase run at each location remained the same as described in experiment one. Experiment three will be referred to as “dual AFOV”.

The pop out distracter effect on the dual AFOV was investigated in experiment 4. One of the distracter locations was replaced with a pop out distracter (red ring) (Fig. 1 – bottom right panel). This experiment will be referred to as “dual AFOV with pop out distracter”.

The pop distracter condition was considered to be too difficult for some participants to perform as the first experiment; therefore, the order of the experiments was not randomized or counterbalanced. As such, practice effects could play a role but the opportunity to learn remained identical for all participants.

The inverse of the average presentation time in seconds for each eccentricity was log transformed and reported in terms of “viewing efficiency”.14,15

The logarithmic transformation, as suggested by Coeckelbergh et al.,15 made the distribution normal (Kolmogorov–Smirnov test, d=0.1, p>0.05) and allowed the use of parametric statistics to perform the analysis.

A repeated measures ANOVA was performed on the log transformed data ([2 tasks; pop out distracter vs. no pop out]×Eccentricity [4, 8 and 12°]) for the standard AFOV and AFOV with pop out distracter (experiments 1 and 2). Comparison between standard AFOV and dual task AFOV (experiments 1 and 3) was also done using a repeated measures ANOVA ([2 tasks; standard AFOV without pop out distracter vs. dual task AFOV]×Eccentricity [4, 8 and 12°]). Similarly the same type of analysis was used for conditions comparing the standard AFOV with pop out distracter and the dual task AFOV with pop out distracter (experiment 2 and 4). Age was considered the between-subject variable in all cases. A post hoc analysis with a Bonferroni correction was used to compare the differences between the means. The p values reported are Huynh–Feldt corrected in cases where the assumption of ANOVA with respect to sphericity was violated.

The results of the first experiment (standard AFOV) show that younger participants have better viewing efficiency than the older individuals at all three eccentricities. This could be due to different search strategies being used by the two age groups when identifying targets. Conventionally, parallel processing refers to visual search where all the information is processed in parallel (at the same time) and involves the preattentive stage.20,21 Such processing usually occurs when the target has one or more feature that is unique from all the distracters The target pops out from the background and can be located in very short presentation times. In serial processing, each item or area in the display is scanned sequentially. Serial processing occurs when more features of the target are shared by the distracters and the search is referred to as conjunction search.21,22 The similarity of the target and distracters plays a role in determining whether the search is parallel or serial. More recent models of visual search propose that a search could be characterized as “efficient” or “inefficient”.23,24 An efficient search is one where the initial stage is able to guide the attention appropriately so that very few locations need to be searched in the subsequent stage. Inefficient searches are those where the initial processing does not guide attention to a particular location, resulting in many more areas being searched before termination of the search. In a visual search task, some attributes of the stimulus such as color, motion, orientation, and size are “undoubtful attributes”24 that are certain to capture attention or guide the attention process to locate a target. Other attributes such as shape, closure, and Vernier offsets are considered “probable attributes”, which may capture attention, although not always.24 In the AFOV (standard), the target is different from the distracters in closure, and since this is a “probable attribute”, the identification of the target can either be an outcome of efficient or inefficient visual searches. It is likely that, as the stimulus in our conditions was a probable attribute, the older participants performed inefficient searches resulting in reduced viewing efficiency compared to the younger participants.

In our experiment we also found that the viewing efficiency decreased with increasing eccentricity for both younger and older participants. However, the eccentricity effect is greater for the younger than the older individuals, which is probably because the older people perform less efficient searches at all eccentricities. This is similar to what other researchers have observed.14,15 The reduced saliency differences between target and the distracter17,25 could be responsible for impeding the search performance. Another reason for the poorer performance of older individuals could be the need to make eye movements to identify the target. Scialfa et al.25 report that older participants made two to three times more saccades than the younger group, in a study of eye movements and age. Another recent study26 measured eye movements during a manual tracking task in which adjustments were made using a joystick to keep a cursor (which was presented eccentrically) in the middle of the display. This study also found that older people compensate for their reduced functional field of view by making more illicit saccades. Although we do not have data to support this claim, it is highly likely that the older individuals made more eye movements in a serial situation where each group of locations was scanned one after another.

In experiment 2 (standard AFOV with pop out distracter) we found that the presence of the pop out distracter (the red ring) resulted in reduced viewing efficiency for younger individuals for targets near the central location. One possibility is that younger participants started their search from the center and the presence of a color distracter target at a different location impeded their search performance. This would be likely as the color attribute has a stronger influence than the “closure” attribute in attracting or guiding attention.24 We then have to ask why the pop out did not have an impact at the 8 and 12° eccentricities. The probable reason is that at these eccentricities the younger participants were already undertaking more inefficient “serial” searches, as the target saliency is not very high. We speculate that, in conditions where participants already scan more locations to identify the target, the pop out distracter itself will have little or no effect on the total time taken to identify the target. This result is rather surprising, as heterogeneous distracters are seen to produce higher error rates on UFOV.25 However, in a UFOV, the condition is formulated for efficient searches and the outcome is binary, i.e. participants perform the task with lower or higher error rates. Similarly, if the older individuals are already making inefficient visual searches in the standard AFOV, then the presence of the pop out distracter will not result in increased presentation times. Colcombe et al.27and Kramer et al.8 also found that the presence of an onset (target appearing abruptly) or colored distracter did not affect their older group more than the younger individuals. They attribute their finding to goal directed behavior and the ability to ignore the irrelevant distracter being intact or not changing with age. In studies of UFOV and AFOV, they find that the target identification at peripheral locations resulted in more wrong responses or reduced visual efficiency as we find in this study.

The results of experiments 3 and 4 assess viewing efficiency of the AFOV in dual task conditions with and without the pop out distracter. Similar to experiments 1 and 2, a significant impact of age was observed, but no effect of the distracter or the additional task. The inclusion of the central task ensures that participants start their search from the central location. Moreover, if the participants were inaccurate on the central task, the trial was put back into the sequence of the staircase.

Studies that have investigated visual search with divided attention tasks have shown that older people perform more poorly than their younger counterparts.10,11 The differences between the age groups are thought to be due to greater divided attention costs for the elderly. However, not all studies that utilized UFOV® find greater divided attention costs for the elderly. The presence of distracters has been shown to have a greater impact on performance than the competing central task.12 These results suggest that the mere presence of distracters makes it harder for older individuals to identify the target location.12 Somberg and Salthouse28 suggest that divided attention costs may be nullified if the baseline performances are equated between younger and older individuals. When they made this normalization, the older participants were seen to have no greater divided attention cost than the younger participants.

The viewing efficiency we observe in this study is much lower than that observed in the study by Coeckelbergh et al.15, i.e. the times taken were longer. The use of the backward masking in our study might have resulted in the higher error rates, resulting in increased thresholds.29 The effect of practice may have also influenced the outcome of the current experiments. As the distracters (white rings) and pop out distracter (red ring) are the same color in all trials, participants could learn to ignore the pop out distracter. The order in which the experiments were done was not randomized and therefore participants might have learned to make more efficient searches with ongoing experiments, which may explain the lack of an effect of the dual task or the addition of the colored pop out distracter. In order to test whether the consistent color of the distracter enabled learning, we repeated experiments 2 and 4 but varied the color of the pop out distracter between 10 possible colors. Similar results were found for both groups, showing the same or slightly higher (especially older group) viewing efficiency compared to their performance in Expt 2 and Expt 4. This suggests that practice plays a role in learning to disregard distracters when assessing functional field of view and may override the effect of clutter or pop out stimuli.

The study has limitations due to the small sample size and the lack of counterbalancing the conditions. Eye movements were not measured and therefore no conclusions can be drawn with respect to where participants were actually looking. It does, however, provide valuable information of how the functional field of view changes for different scenarios and the role of practice. In summary, viewing efficiency as described by AFOV is affected by age. The utilization of efficient vs. inefficient searches is suggested as the reason for the differences found between age groups. Elderly participants have more difficulty in disregarding irrelevant distracters and resort to an inefficient search strategy. Older peoples’ performance in the presence of distracters is reduced by a constant amount compared to younger observers, but the addition of a dual task or a pop out distracter has little effect. An important aspect of this study is the finding that older or younger individuals are not affected significantly by the presence of the irrelevant pop out distracter. This has implications, as with ensuing trials individuals are able to ignore the pop out distracter irrespective of the location in the visual field. In situations such as driving or other situations of hazard avoidance, the presence of irrelevant pop out distracter does not impair the search performance beyond what is found with general clutter. This is encouraging, as it implies that the deficit in older people is a constant reduction, rather than increasing with increased stimulus complexity, and the practice effects suggest that reduced performance of older individuals may be trainable.

The results obtained are relevant to everyday tasks such as driving and walking. For example, a new distraction, such as a new bill board, would not be expected to affect an older individual more than their younger counterpart while driving. In the vision literature, the use of a test such as the UFOV has been suggested to identify the at-risk driver. Parameters that affect tests such as AFOV and UFOV have to be well understood before applying such tests in a real world scenario. Our experiment has highlighted how some of these parameters affect the AFOV.

This work was supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Canadian Foundation for Innovation (CFI), Canada Research Chair (CRC), and the National Institute on Disability and Rehabilitation Research (NIDRR) through the Rehabilitation Engineering Research Center on Universal Design and the Built Environment (RERC).

The authors have no conflicts of interest to declare.