Neuroscience Letters 566 (2014) 27–31
Contents lists available at ScienceDirect
Neuroscience Letters journal homepage: www.elsevier.com/locate/neulet
Is the size of the useful field of view affected by postural demands associated with standing and stepping? James G. Reed-Jones a , Rebecca J. Reed-Jones a,∗ , Mark A. Hollands b a b
Department of Applied Human Sciences, Faculty of Science, University of Prince Edward Island, Canada Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
h i g h l i g h t s • • • • •
Examined the effects of posture on useful field of view (UFOV). UFOV was measured while seated, standing and stepping in place. Divided-attention performance significantly reduced while stepping in place. Results suggest size of UFOV declines with postural demand. Important practical implications for testing UFOV.
a r t i c l e
i n f o
Article history: Received 25 September 2013 Received in revised form 31 January 2014 Accepted 18 February 2014 Keywords: Useful field of view Postural control Visual attention Cognitive load Divided-attention
a b s t r a c t The useful field of view (UFOV) is the visual area from which information is obtained at a brief glance. While studies have examined the effects of increased cognitive load on the visual field, no one has specifically looked at the effects of postural control or locomotor activity on the UFOV. The current study aimed to examine the effects of postural demand and locomotor activity on UFOV performance in healthy young adults. Eleven participants were tested on three modified UFOV tasks (central processing, peripheral processing, and divided-attention) while seated, standing, and stepping in place. Across all postural conditions, participants showed no difference in their central or peripheral processing. However, in the divided-attention task (reporting the letter in central vision and target location in peripheral vision amongst distracter items) a main effect of posture condition on peripheral target accuracy was found for targets at 57◦ of eccentricity (p = .037). The mean accuracy reduced from 80.5% (standing) to 74% (seated) to 56.3% (stepping). These findings show that postural demands do affect UFOV divided-attention performance. In particular, the size of the useful field of view significantly decreases when stepping. This finding has important implications for how the results of a UFOV test are used to evaluate the general size of the UFOV during varying activities, as the traditional seated test procedure may overestimate the size of the UFOV during locomotor activities. © 2014 Elsevier Ireland Ltd. All rights reserved.
1. Introduction The useful field of view (UFOV) is the visual area from which useful information can be extracted from a brief glance or fixation [1]. Reductions in the UFOV occur with aging [1]. Reduced UFOV performance, particularly divided-attention sub-tests, correlates with increased vehicular crash risk, obstacle collisions, and propensity for falls [2–5]. While studies have examined the effects of increased
∗ Corresponding author at: Department of Applied Human Sciences, Faculty of Science, University of Prince Edward Island, 550 University Ave, Charlottetown, PE C1A 4P3, Canada. Tel.: +1 902 628 4358. E-mail address: [email protected] (R.J. Reed-Jones). http://dx.doi.org/10.1016/j.neulet.2014.02.031 0304-3940/© 2014 Elsevier Ireland Ltd. All rights reserved.
cognitive load on the visual field [6–8], and the effects that the size of the visual field has on postural control [9], no one has specifically looked at the effects of postural control or locomotor activity on the UFOV. A vast body of research also exists showing that postural control can affect cognitive function and vice versa. Dual tasks that involve concurrent postural and cognitive task performance, demonstrate that with increased postural control demand, the greater the need for cognitive involvement to maintain stability [10–12]. Research on postural task and cognitive task interplay have used cognitive tasks involving verbal memory, visual memory, and auditory memory but have not investigated the changes that occur in visual attention with increased postural demand [13–15].
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J.G. Reed-Jones et al. / Neuroscience Letters 566 (2014) 27–31
If the visual field varies as a function of postural control demand, then changes to the visual field could be task-specific. Understanding the relationship between posture and the UFOV is of particular importance given that decline in divided-attention performance occurs with age and is associated with increased fall risk in older adults [1,4,5]. Knowledge of a relationship between certain postural and locomotor activities and the UFOV could lead to specific recommendations for older adults during certain activities in an attempt to reduce the risk of a fall related injury. Therefore, the purpose of the current study was to examine the effects of postural demand and locomotor activity on useful visual field performance, as measured by a modified UFOV task, in healthy young adults. We hypothesized that as the demand for postural control increased, performance on the modified UFOV task (specifically divided-attention) would decrease. As a result, we would observe the best performance on the divided-attention task while seated, followed by standing, and finally the lowest performance while stepping in place. 2. Methods Eleven participants were recruited from the graduate student population of the University. All participants were healthy adults ranging from 23 to 33 years (M = 28.4, SD = 3.8; 6 males, 5 females). All participants had corrected (contact lenses only) or uncorrected near 20/20 acuity. Ethics Committee approval from the university was obtained for human participant involvement and the experiment was carried out in accordance with the declaration of Helsinki. An ASL eye tracker (Applied Sciences Laboratories, MA, USA) monitored the participants’ eye position during testing. It consisted of an acrylic monocle suspended under the left eye and a high-speed camera, which monitored the participants’ eye position, mounted onto a headband. The eye tracker did not occlude any of the visual field while worn. The eye tracker output included crosshairs, representing gaze position, overlaid onto a video of the area directly in front of the participant. The video was recorded at 30 Hz and was used to monitor participants’ gaze fixation compliance during
UFOV testing. To determine cadence, retroreflective markers were placed on each participant’s heels, and a video camera recorded their footfalls at 30 Hz. The modified UFOV tasks were back projected onto a 136 cm (W) × 120 cm (H) screen. Viewing distance from the screen was 50 cm and the central fixation point was centered on the participants’ eye line for each task (to accommodate changes in height between sitting and standing). For each of the three UFOV tasks, the visual display consisted of a gray background with a white square fixation point (6.7◦ × 6.7◦ ). Task 1, central processing, consisted of one of the four black letters (E, F, H or L) presented within the central fixation box. Each letter measured 3.5◦ × 3.5◦ . For task 2, peripheral processing, one black circular target (3.5◦ in diameter) was presented at 18◦ , 37◦ , or 57◦ of eccentricity in one of the 24 possible locations encircling the central target. In addition, 23 white rings (4.7◦ in diameter) were presented as distracters. For task 3, dividedattention, both the central letter discrimination and the peripheral target localization were presented simultaneously. Each task consisted of 16 trials. See Fig. 1 for a visual representation of the three tasks. 2.1. Procedure Following completion of the consent and screening forms, the eye tracker was fitted and calibrated, and the video camera was set to record the participant’s feet. Each participant then completed the three modified UFOV tasks while seated, standing, and stepping in place (16 trials for each task in each posture). For stepping in place, the participant was instructed to step at a comfortable self-selected rate. The task/postural condition combinations were conducted in a random order. However, each task was structured in the same manner. First, the participant adopted the position of the task and the display was adjusted to match the eye line of the participant (seated, standing, or stepping). The tasks were then conducted, each using the following order. 1. The gray background and fixation box screen was displayed.
Fig. 1. Depiction of the experimental stimuli over time. At time 3, the three different processing tests are illustrated: central, peripheral and divided-attention.
The stimulus presentation time of 63 ms was chosen because it was long enough for a target to be visible but short enough that a ballistic eye movement could not be made to a target. Once all three tasks were complete for each postural condition, the participant was debriefed and asked if they had any questions. The total duration of the experiment was approximately 1 h. 2.2. Statistical analysis In the following analyses, all UFOV tasks shared the same definition of accuracy. Specifically, accuracy was the number of targets correctly identified across all trials, expressed as a percentage. For example, for the central processing task while stepping if the central target was correctly identified in 10 of the 16 trials, the score for that task was 62.5%. For the central and peripheral processing tasks, accuracy was 100% across all posture conditions. Therefore, no statistics were run for these tasks. For the divided-attention processing task a repeated measures ANOVA was conducted with two independent variables; Eccentricity with three levels (18◦ , 37◦ , 57◦ ) and Posture with three levels (sitting, standing, stepping). For this task, no statistics were conducted on the central processing portion, as accuracy was 100% for all participants. Cadence (step rate) on the stepping in place posture was assessed using a repeated measure ANOVA with the independent variable, Task with three levels (central, peripheral and divided-attention). Alpha level was set at 0.05 for all analyses with Bonferroni corrected pair-wise comparisons. 3. Results
100 90 80 70 60 50 40 30 20 10 0
†
29
† *
†
* Central 18° 37° 57°
Sing
Standing Condion
Stepping
Fig. 2. Summary of the results (M ± SEM) of the divided-attention tasks. Significantly greater errors were observed at larger eccentricities (†). Significantly lower accuracy at 57◦ of eccentricity was observed during stepping compared to standing (*).
Cadence in Steps per Minute
2. The word ‘GO!’ in black lettering on a green background was presented in the fixation box (for 1 s) to indicate the beginning of the trial and to prompt the participant to fixate (the participant was instructed to fixate from this point until the response screen). 3. The stimulus was presented for 63 ms. 4. A masking field displaying white and black squares was presented for 1 s. 5. The response prompt screen was displayed with the four letter choices in the center of the screen and numbers were displayed indicating the potential peripheral target positions. 6. The participant verbally responded with the letter (central processing), number (peripheral processing), or letter number combination (divided-attention processing) corresponded with their answer. 7. The next trial began.
Accuracy %
J.G. Reed-Jones et al. / Neuroscience Letters 566 (2014) 27–31
124 122 120 118 116 114 112 110 108 106 104 102 Central Only
†
†
Peripheral Only
Divided-aenon
Processing Task Fig. 3. Mean stepping cadence for each visual task (±SEM). A significant increase in step rate was observed during the peripheral and divided tasks compared to the central task (†).
standing (p = 1.00). Overall, mean accuracy on the peripheral component of the divided-attention task at 57◦ of eccentricity reduced from 80.5% when standing to 74% when seated to 56.3% when stepping in place (see Fig. 2). 3.3. Stepping cadence A significant main effect of task was observed on stepping rate (p < 0.001; 2 = 0.77). Post hoc testing showed that stepping rates during the peripheral only task and divided-attention task were significantly greater than during the central only task (p = 0.002; see Fig. 3).
3.1. Gaze fixation Compliance with the gaze fixation instruction was confirmed using the eye tracker. Examination of gaze position (cross hairs) revealed that participants maintained central fixation during stimulus presentation (63 ms time period) for all experimental trials. 3.2. Modified UFOV tasks For the divided-attention task, a significant main effect of eccentricity on accuracy was observed (p = 0.01; 2 = 0.66) with lower accuracies occurring at greater eccentricities (see Fig. 2). A significant interaction between posture and eccentricity (p = 0.049; 2 = 0.21) was also observed (see Fig. 2). Post hoc testing within each eccentricity revealed a main effect of posture at 57◦ of eccentricity (p = 0.037; 2 = 0.28). Stepping in place resulted in significantly greater divided attention error than during standing (p = 0.02; 2 = 0.28). No significant difference was found between sitting and
4. Discussion The current study examined the interplay between increased postural control demand and the size of the useful field of view in healthy young adults. Using healthy young adults, instead of older adults, allowed us to examine the effects of postural demand on UFOV performance without having to address the changes to the UFOV associated with aging itself. The central and peripheral only tasks were used as controls and were found to have 100% accuracy during all postures. These results were expected, and confirmed that each posture did not interfere with viewing the screen. As a result, any decrements in performance on the divided-attention task could be attributed to the interplay between the cognitive demand required for the divided-attention visual task and the postural tasks. How then does the attentional demand of a postural task influence the visual field? Researchers in psychology have noted a
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J.G. Reed-Jones et al. / Neuroscience Letters 566 (2014) 27–31
phenomenon termed cognitive tunneling where the peripheral visual field shrinks with increased cognitive load [7,8]. If a given postural task incurs cognitive resources (a.k.a. cognitive load), we would expect that the size of the useful field of view would reduce in that postural task. Based on this logic, we hypothesized that as the complexity of the postural control task increased the UFOV would decrease, affecting peripheral visual performance. Therefore, in the current study, UFOV performance would be at its highest in the seated condition, followed by standing, and finally stepping in place. The results of the study partially supported our hypothesis. Stepping UFOV performance was the lowest of the three postural conditions, however standing UFOV performance was not significantly different from that of seated (Fig. 2). These results indicate that postural demand can significantly affect UFOV divided-attention performance in the periphery. However, that this relationship is not linear as there is a slight increase in dividedattention of the UFOV from sitting to standing. Dual task paradigms where participants need to control balance while performing a second attentional demanding cognitive task (e.g. mental arithmetic), show that reductions in postural control performance and/or cognitive task performance can occur [10–14]. The degree to which one task influences the other can vary group to group and depend on the age of the participants as well as their balance ability [10]. The postural task itself influences the decline in cognitive task performance; the greater the complexity or challenge to the balance system, the more cognitive resources are needed to maintain stability resulting in a decline in cognitive task performance. For example, Lajoie et al. [15] found that reaction times for an auditory task varied as a function of the postural task. Reaction times were fastest when seated and slowest when standing and walking, with the slowest reactions during reduced base of support conditions (walking). An interesting finding of the current study is that standing control did not reduce UFOV performance. One explanation for this result is that in a young healthy population, standing postural control (double support stance) may present a low postural threat and therefore require little cognitive influence. This leaves the visual field unaffected by cognitive load during this task. Both peripheral and central visual cues contribute to orientation information during standing. However, research has suggested that peripheral information is more important during postural control than central (foveal) information [9,16]. As such, the peripheral visual system and divided attention may up regulate during standing postural control as compared to seated postural control. When moving to stepping in place however, due to the increased complexity of the task (including a great deal of single support stance), the attentional demands for stability outweigh the demands for the UFOV task. As a result, a sacrifice in UFOV performance occurred in order to compensate for the increased attentional demands of the stepping task. Reciprocally, increasing the difficulty of the visual task (by adding peripheral targets) may divert attention away from regulation of stepping on the spot as observed with the greater step cadence in the peripheral only and divided attention tasks. In addition, stepping in place requires greater demands for gaze stabilization (via the vestibular ocular and vestibulo-colic reflexes) resultant of the oscillations induced by the stepping movement. Increased involvement of the vestibular system for coordinating eye and head movement to provide stability also competes for attentional resources during dual-tasks [17]. Therefore, not only may stepping in place pose postural control demands (body segment control under reduced base of support) on attention but also may pose oculomotor and other sensory integration demands. One argument to the interpretation of the results of the current study is that peripheral target accuracy resulted from the inability to stabilize the peripheral image during stepping in place. However,
during the peripheral only task, target accuracy while stepping in place was 100%. This perfect accuracy was not the result of any eye movements made to the peripheral target in this task as participants were instructed to fixate on the central box (though no letter was presented in the box during the peripheral only task) and fixation compliance was measured by the eye tracker. Therefore, we can conclude that reduced accuracy during the divided-attention task while stepping in place was not the result of poor peripheral stabilization but rather a result of the reduced peripheral field during the divided-attention task. A limitation of the current study was the nature of the eye tracking data collected. While the gaze data recorded did provide a means to ensure participant compliance with the visual task, it did not allow sufficient temporal resolution to determine variability of gaze fixation within the center target (6.7◦ × 6.7◦ ) during the different postural tasks. Given the current findings, examination of gaze stability under these conditions warrants further study. 5. Conclusions The implications of this initial study are important. We observed that the size of the useful visual field declines with postural control demands in a healthy young adult population. In older adults who experience decreased UFOV size [1] and postural control [18] with age, these affects may magnify. This is an important consideration when testing individuals on their UFOV as results may not reflect the true UFOV in dual tasks, particularly those of a locomotor nature. Clearly, further research examining older adults under conditions similar to those presented by this study may reveal interesting results regarding the nature of the useful field of view, visual attention, and postural control during the aging process. Conflict of interest None of the authors of the above manuscript have declared conflict of interest which may arise from being named as an author on the manuscript. References [1] K.K. Ball, B.L. Beard, D.L. Roekner, R.L. Miller, D.S. Griggs, Age and visual search: expanding the useful field of view, Journal of the Optical Society 5 (12) (1988) 2210–2219. [2] K. Ball, C. Owsley, M.E. Sloane, D.L. Roekner, J.R. Bruni, Visual attention problems as a predictor of vehicle crashes on older drivers, Investigative Ophthalmology & Visual Science 34 (1993) 3110–3123. [3] C. Owsley, K. Ball, G.J. McGwin, M.E. Sloane, D.L. Roenker, M.F. White, E.T. Overley, Visual processing impairment and risk of motor vehicle crash among older adults, JAMA 279 (14) (1998) 1083–1088. [4] A.T. Broman, S.K. West, B. Munoz, K. Bandeen-Roche, G.S. Rubin, K.A. Turano, Divided visual attention as a predictor of bumping while walking: the salisbury eye evaluation, Investigative Ophthalmology & Visual Science 45 (9) (2004) 2955–2960. [5] D.E. Vance, K.K. Ball, D.L. Roenker, V.G. Wadley, J.D. Edwards, G.M. Cissell, Predictors of falling in older Maryland drivers: a structural-equation model, Journal of Aging and Physical Activity 14 (3) (2006) 254–269. [6] L.J. Williams, Cognitive load and functional field of view, Human Factors 24 (1982) 683–692. [7] E.M. Rantanen, J.H. Goldberg, The effect of mental workload on the visual field size and shape, Ergonomics 42 (6) (1999) 816–834. [8] P. Atchley, J. Dressel, Conversation limits the functional field of view, Human Factors 46 (4) (2011) 664–673. [9] J.W. Streepey, R.V. Kenyon, E.A. Keshner, Field of view and base of support width influence responses to visual stimuli during quiet stance, Gait and Posture 25 (49) (2007) 55. [10] M. Wollacott, A. Shumway-Cooke, Attention and the control of posture and gait: a review of an emerging area of research, Gait and Posture 16 (2002) 1–14. [11] E.V. Fraizer, M. Subhobrata, Methodological and interpretive issues in posture cognition dual-tasking in upright stance, Gait and Posture 27 (2008) 271–279. [12] B.E. Maki, W.E. McIlroy, Cognitive demands and cortical control of human balance recovery reactions, Journal of Neural Transmission 114 (2007) 1279– 1296.
J.G. Reed-Jones et al. / Neuroscience Letters 566 (2014) 27–31 [13] M.C. Dault, J.S. Frank, F. Allard, Influence of a visuo-spatial, verbal and central executive working memory task on postural control, Gait and Posture 14 (2) (2001) 110–116. [14] B. Kerr, S.M. Condon, L.A. McDonald, Cognitive spatial processing and the regulation of posture, Journal of Experimental Psychology 11 (1985) 617– 622. [15] Y. Lajoie, N. Teasdale, C. Bard, M. Fleury, Attentional demands for static and dynamic equilibrium, Experimental Brain Research 97 (1993) 139–144.
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[16] A. Berencsi, M. Ishihara, K. Imanaka, The functional role of central and peripheral vision in the control of posture, Human Movement Science 24 (2005) 689–709. [17] J.M. Furman, M.L. Muller, M.S. Redfern, J.R. Jennings, Visual-vestibular stimulation interferes with information processing in young and older humans, Experimental Brain Research 152 (2003) 383–392. [18] B.E. Maki, W.E. McIlroy, Postural control in the older adult, Clinical Geriatric Medicine 12 (4) (1996) 635–658.
Contents lists available at ScienceDirect
Neuroscience Letters journal homepage: www.elsevier.com/locate/neulet
Is the size of the useful field of view affected by postural demands associated with standing and stepping? James G. Reed-Jones a , Rebecca J. Reed-Jones a,∗ , Mark A. Hollands b a b
Department of Applied Human Sciences, Faculty of Science, University of Prince Edward Island, Canada Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
h i g h l i g h t s • • • • •
Examined the effects of posture on useful field of view (UFOV). UFOV was measured while seated, standing and stepping in place. Divided-attention performance significantly reduced while stepping in place. Results suggest size of UFOV declines with postural demand. Important practical implications for testing UFOV.
a r t i c l e
i n f o
Article history: Received 25 September 2013 Received in revised form 31 January 2014 Accepted 18 February 2014 Keywords: Useful field of view Postural control Visual attention Cognitive load Divided-attention
a b s t r a c t The useful field of view (UFOV) is the visual area from which information is obtained at a brief glance. While studies have examined the effects of increased cognitive load on the visual field, no one has specifically looked at the effects of postural control or locomotor activity on the UFOV. The current study aimed to examine the effects of postural demand and locomotor activity on UFOV performance in healthy young adults. Eleven participants were tested on three modified UFOV tasks (central processing, peripheral processing, and divided-attention) while seated, standing, and stepping in place. Across all postural conditions, participants showed no difference in their central or peripheral processing. However, in the divided-attention task (reporting the letter in central vision and target location in peripheral vision amongst distracter items) a main effect of posture condition on peripheral target accuracy was found for targets at 57◦ of eccentricity (p = .037). The mean accuracy reduced from 80.5% (standing) to 74% (seated) to 56.3% (stepping). These findings show that postural demands do affect UFOV divided-attention performance. In particular, the size of the useful field of view significantly decreases when stepping. This finding has important implications for how the results of a UFOV test are used to evaluate the general size of the UFOV during varying activities, as the traditional seated test procedure may overestimate the size of the UFOV during locomotor activities. © 2014 Elsevier Ireland Ltd. All rights reserved.
1. Introduction The useful field of view (UFOV) is the visual area from which useful information can be extracted from a brief glance or fixation [1]. Reductions in the UFOV occur with aging [1]. Reduced UFOV performance, particularly divided-attention sub-tests, correlates with increased vehicular crash risk, obstacle collisions, and propensity for falls [2–5]. While studies have examined the effects of increased
∗ Corresponding author at: Department of Applied Human Sciences, Faculty of Science, University of Prince Edward Island, 550 University Ave, Charlottetown, PE C1A 4P3, Canada. Tel.: +1 902 628 4358. E-mail address: [email protected] (R.J. Reed-Jones). http://dx.doi.org/10.1016/j.neulet.2014.02.031 0304-3940/© 2014 Elsevier Ireland Ltd. All rights reserved.
cognitive load on the visual field [6–8], and the effects that the size of the visual field has on postural control [9], no one has specifically looked at the effects of postural control or locomotor activity on the UFOV. A vast body of research also exists showing that postural control can affect cognitive function and vice versa. Dual tasks that involve concurrent postural and cognitive task performance, demonstrate that with increased postural control demand, the greater the need for cognitive involvement to maintain stability [10–12]. Research on postural task and cognitive task interplay have used cognitive tasks involving verbal memory, visual memory, and auditory memory but have not investigated the changes that occur in visual attention with increased postural demand [13–15].
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J.G. Reed-Jones et al. / Neuroscience Letters 566 (2014) 27–31
If the visual field varies as a function of postural control demand, then changes to the visual field could be task-specific. Understanding the relationship between posture and the UFOV is of particular importance given that decline in divided-attention performance occurs with age and is associated with increased fall risk in older adults [1,4,5]. Knowledge of a relationship between certain postural and locomotor activities and the UFOV could lead to specific recommendations for older adults during certain activities in an attempt to reduce the risk of a fall related injury. Therefore, the purpose of the current study was to examine the effects of postural demand and locomotor activity on useful visual field performance, as measured by a modified UFOV task, in healthy young adults. We hypothesized that as the demand for postural control increased, performance on the modified UFOV task (specifically divided-attention) would decrease. As a result, we would observe the best performance on the divided-attention task while seated, followed by standing, and finally the lowest performance while stepping in place. 2. Methods Eleven participants were recruited from the graduate student population of the University. All participants were healthy adults ranging from 23 to 33 years (M = 28.4, SD = 3.8; 6 males, 5 females). All participants had corrected (contact lenses only) or uncorrected near 20/20 acuity. Ethics Committee approval from the university was obtained for human participant involvement and the experiment was carried out in accordance with the declaration of Helsinki. An ASL eye tracker (Applied Sciences Laboratories, MA, USA) monitored the participants’ eye position during testing. It consisted of an acrylic monocle suspended under the left eye and a high-speed camera, which monitored the participants’ eye position, mounted onto a headband. The eye tracker did not occlude any of the visual field while worn. The eye tracker output included crosshairs, representing gaze position, overlaid onto a video of the area directly in front of the participant. The video was recorded at 30 Hz and was used to monitor participants’ gaze fixation compliance during
UFOV testing. To determine cadence, retroreflective markers were placed on each participant’s heels, and a video camera recorded their footfalls at 30 Hz. The modified UFOV tasks were back projected onto a 136 cm (W) × 120 cm (H) screen. Viewing distance from the screen was 50 cm and the central fixation point was centered on the participants’ eye line for each task (to accommodate changes in height between sitting and standing). For each of the three UFOV tasks, the visual display consisted of a gray background with a white square fixation point (6.7◦ × 6.7◦ ). Task 1, central processing, consisted of one of the four black letters (E, F, H or L) presented within the central fixation box. Each letter measured 3.5◦ × 3.5◦ . For task 2, peripheral processing, one black circular target (3.5◦ in diameter) was presented at 18◦ , 37◦ , or 57◦ of eccentricity in one of the 24 possible locations encircling the central target. In addition, 23 white rings (4.7◦ in diameter) were presented as distracters. For task 3, dividedattention, both the central letter discrimination and the peripheral target localization were presented simultaneously. Each task consisted of 16 trials. See Fig. 1 for a visual representation of the three tasks. 2.1. Procedure Following completion of the consent and screening forms, the eye tracker was fitted and calibrated, and the video camera was set to record the participant’s feet. Each participant then completed the three modified UFOV tasks while seated, standing, and stepping in place (16 trials for each task in each posture). For stepping in place, the participant was instructed to step at a comfortable self-selected rate. The task/postural condition combinations were conducted in a random order. However, each task was structured in the same manner. First, the participant adopted the position of the task and the display was adjusted to match the eye line of the participant (seated, standing, or stepping). The tasks were then conducted, each using the following order. 1. The gray background and fixation box screen was displayed.
Fig. 1. Depiction of the experimental stimuli over time. At time 3, the three different processing tests are illustrated: central, peripheral and divided-attention.
The stimulus presentation time of 63 ms was chosen because it was long enough for a target to be visible but short enough that a ballistic eye movement could not be made to a target. Once all three tasks were complete for each postural condition, the participant was debriefed and asked if they had any questions. The total duration of the experiment was approximately 1 h. 2.2. Statistical analysis In the following analyses, all UFOV tasks shared the same definition of accuracy. Specifically, accuracy was the number of targets correctly identified across all trials, expressed as a percentage. For example, for the central processing task while stepping if the central target was correctly identified in 10 of the 16 trials, the score for that task was 62.5%. For the central and peripheral processing tasks, accuracy was 100% across all posture conditions. Therefore, no statistics were run for these tasks. For the divided-attention processing task a repeated measures ANOVA was conducted with two independent variables; Eccentricity with three levels (18◦ , 37◦ , 57◦ ) and Posture with three levels (sitting, standing, stepping). For this task, no statistics were conducted on the central processing portion, as accuracy was 100% for all participants. Cadence (step rate) on the stepping in place posture was assessed using a repeated measure ANOVA with the independent variable, Task with three levels (central, peripheral and divided-attention). Alpha level was set at 0.05 for all analyses with Bonferroni corrected pair-wise comparisons. 3. Results
100 90 80 70 60 50 40 30 20 10 0
†
29
† *
†
* Central 18° 37° 57°
Sing
Standing Condion
Stepping
Fig. 2. Summary of the results (M ± SEM) of the divided-attention tasks. Significantly greater errors were observed at larger eccentricities (†). Significantly lower accuracy at 57◦ of eccentricity was observed during stepping compared to standing (*).
Cadence in Steps per Minute
2. The word ‘GO!’ in black lettering on a green background was presented in the fixation box (for 1 s) to indicate the beginning of the trial and to prompt the participant to fixate (the participant was instructed to fixate from this point until the response screen). 3. The stimulus was presented for 63 ms. 4. A masking field displaying white and black squares was presented for 1 s. 5. The response prompt screen was displayed with the four letter choices in the center of the screen and numbers were displayed indicating the potential peripheral target positions. 6. The participant verbally responded with the letter (central processing), number (peripheral processing), or letter number combination (divided-attention processing) corresponded with their answer. 7. The next trial began.
Accuracy %
J.G. Reed-Jones et al. / Neuroscience Letters 566 (2014) 27–31
124 122 120 118 116 114 112 110 108 106 104 102 Central Only
†
†
Peripheral Only
Divided-aenon
Processing Task Fig. 3. Mean stepping cadence for each visual task (±SEM). A significant increase in step rate was observed during the peripheral and divided tasks compared to the central task (†).
standing (p = 1.00). Overall, mean accuracy on the peripheral component of the divided-attention task at 57◦ of eccentricity reduced from 80.5% when standing to 74% when seated to 56.3% when stepping in place (see Fig. 2). 3.3. Stepping cadence A significant main effect of task was observed on stepping rate (p < 0.001; 2 = 0.77). Post hoc testing showed that stepping rates during the peripheral only task and divided-attention task were significantly greater than during the central only task (p = 0.002; see Fig. 3).
3.1. Gaze fixation Compliance with the gaze fixation instruction was confirmed using the eye tracker. Examination of gaze position (cross hairs) revealed that participants maintained central fixation during stimulus presentation (63 ms time period) for all experimental trials. 3.2. Modified UFOV tasks For the divided-attention task, a significant main effect of eccentricity on accuracy was observed (p = 0.01; 2 = 0.66) with lower accuracies occurring at greater eccentricities (see Fig. 2). A significant interaction between posture and eccentricity (p = 0.049; 2 = 0.21) was also observed (see Fig. 2). Post hoc testing within each eccentricity revealed a main effect of posture at 57◦ of eccentricity (p = 0.037; 2 = 0.28). Stepping in place resulted in significantly greater divided attention error than during standing (p = 0.02; 2 = 0.28). No significant difference was found between sitting and
4. Discussion The current study examined the interplay between increased postural control demand and the size of the useful field of view in healthy young adults. Using healthy young adults, instead of older adults, allowed us to examine the effects of postural demand on UFOV performance without having to address the changes to the UFOV associated with aging itself. The central and peripheral only tasks were used as controls and were found to have 100% accuracy during all postures. These results were expected, and confirmed that each posture did not interfere with viewing the screen. As a result, any decrements in performance on the divided-attention task could be attributed to the interplay between the cognitive demand required for the divided-attention visual task and the postural tasks. How then does the attentional demand of a postural task influence the visual field? Researchers in psychology have noted a
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phenomenon termed cognitive tunneling where the peripheral visual field shrinks with increased cognitive load [7,8]. If a given postural task incurs cognitive resources (a.k.a. cognitive load), we would expect that the size of the useful field of view would reduce in that postural task. Based on this logic, we hypothesized that as the complexity of the postural control task increased the UFOV would decrease, affecting peripheral visual performance. Therefore, in the current study, UFOV performance would be at its highest in the seated condition, followed by standing, and finally stepping in place. The results of the study partially supported our hypothesis. Stepping UFOV performance was the lowest of the three postural conditions, however standing UFOV performance was not significantly different from that of seated (Fig. 2). These results indicate that postural demand can significantly affect UFOV divided-attention performance in the periphery. However, that this relationship is not linear as there is a slight increase in dividedattention of the UFOV from sitting to standing. Dual task paradigms where participants need to control balance while performing a second attentional demanding cognitive task (e.g. mental arithmetic), show that reductions in postural control performance and/or cognitive task performance can occur [10–14]. The degree to which one task influences the other can vary group to group and depend on the age of the participants as well as their balance ability [10]. The postural task itself influences the decline in cognitive task performance; the greater the complexity or challenge to the balance system, the more cognitive resources are needed to maintain stability resulting in a decline in cognitive task performance. For example, Lajoie et al. [15] found that reaction times for an auditory task varied as a function of the postural task. Reaction times were fastest when seated and slowest when standing and walking, with the slowest reactions during reduced base of support conditions (walking). An interesting finding of the current study is that standing control did not reduce UFOV performance. One explanation for this result is that in a young healthy population, standing postural control (double support stance) may present a low postural threat and therefore require little cognitive influence. This leaves the visual field unaffected by cognitive load during this task. Both peripheral and central visual cues contribute to orientation information during standing. However, research has suggested that peripheral information is more important during postural control than central (foveal) information [9,16]. As such, the peripheral visual system and divided attention may up regulate during standing postural control as compared to seated postural control. When moving to stepping in place however, due to the increased complexity of the task (including a great deal of single support stance), the attentional demands for stability outweigh the demands for the UFOV task. As a result, a sacrifice in UFOV performance occurred in order to compensate for the increased attentional demands of the stepping task. Reciprocally, increasing the difficulty of the visual task (by adding peripheral targets) may divert attention away from regulation of stepping on the spot as observed with the greater step cadence in the peripheral only and divided attention tasks. In addition, stepping in place requires greater demands for gaze stabilization (via the vestibular ocular and vestibulo-colic reflexes) resultant of the oscillations induced by the stepping movement. Increased involvement of the vestibular system for coordinating eye and head movement to provide stability also competes for attentional resources during dual-tasks [17]. Therefore, not only may stepping in place pose postural control demands (body segment control under reduced base of support) on attention but also may pose oculomotor and other sensory integration demands. One argument to the interpretation of the results of the current study is that peripheral target accuracy resulted from the inability to stabilize the peripheral image during stepping in place. However,
during the peripheral only task, target accuracy while stepping in place was 100%. This perfect accuracy was not the result of any eye movements made to the peripheral target in this task as participants were instructed to fixate on the central box (though no letter was presented in the box during the peripheral only task) and fixation compliance was measured by the eye tracker. Therefore, we can conclude that reduced accuracy during the divided-attention task while stepping in place was not the result of poor peripheral stabilization but rather a result of the reduced peripheral field during the divided-attention task. A limitation of the current study was the nature of the eye tracking data collected. While the gaze data recorded did provide a means to ensure participant compliance with the visual task, it did not allow sufficient temporal resolution to determine variability of gaze fixation within the center target (6.7◦ × 6.7◦ ) during the different postural tasks. Given the current findings, examination of gaze stability under these conditions warrants further study. 5. Conclusions The implications of this initial study are important. We observed that the size of the useful visual field declines with postural control demands in a healthy young adult population. In older adults who experience decreased UFOV size [1] and postural control [18] with age, these affects may magnify. This is an important consideration when testing individuals on their UFOV as results may not reflect the true UFOV in dual tasks, particularly those of a locomotor nature. Clearly, further research examining older adults under conditions similar to those presented by this study may reveal interesting results regarding the nature of the useful field of view, visual attention, and postural control during the aging process. Conflict of interest None of the authors of the above manuscript have declared conflict of interest which may arise from being named as an author on the manuscript. References [1] K.K. Ball, B.L. Beard, D.L. Roekner, R.L. Miller, D.S. Griggs, Age and visual search: expanding the useful field of view, Journal of the Optical Society 5 (12) (1988) 2210–2219. [2] K. Ball, C. Owsley, M.E. Sloane, D.L. Roekner, J.R. Bruni, Visual attention problems as a predictor of vehicle crashes on older drivers, Investigative Ophthalmology & Visual Science 34 (1993) 3110–3123. [3] C. Owsley, K. Ball, G.J. McGwin, M.E. Sloane, D.L. Roenker, M.F. White, E.T. Overley, Visual processing impairment and risk of motor vehicle crash among older adults, JAMA 279 (14) (1998) 1083–1088. [4] A.T. Broman, S.K. West, B. Munoz, K. Bandeen-Roche, G.S. Rubin, K.A. Turano, Divided visual attention as a predictor of bumping while walking: the salisbury eye evaluation, Investigative Ophthalmology & Visual Science 45 (9) (2004) 2955–2960. [5] D.E. Vance, K.K. Ball, D.L. Roenker, V.G. Wadley, J.D. Edwards, G.M. Cissell, Predictors of falling in older Maryland drivers: a structural-equation model, Journal of Aging and Physical Activity 14 (3) (2006) 254–269. [6] L.J. Williams, Cognitive load and functional field of view, Human Factors 24 (1982) 683–692. [7] E.M. Rantanen, J.H. Goldberg, The effect of mental workload on the visual field size and shape, Ergonomics 42 (6) (1999) 816–834. [8] P. Atchley, J. Dressel, Conversation limits the functional field of view, Human Factors 46 (4) (2011) 664–673. [9] J.W. Streepey, R.V. Kenyon, E.A. Keshner, Field of view and base of support width influence responses to visual stimuli during quiet stance, Gait and Posture 25 (49) (2007) 55. [10] M. Wollacott, A. Shumway-Cooke, Attention and the control of posture and gait: a review of an emerging area of research, Gait and Posture 16 (2002) 1–14. [11] E.V. Fraizer, M. Subhobrata, Methodological and interpretive issues in posture cognition dual-tasking in upright stance, Gait and Posture 27 (2008) 271–279. [12] B.E. Maki, W.E. McIlroy, Cognitive demands and cortical control of human balance recovery reactions, Journal of Neural Transmission 114 (2007) 1279– 1296.
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![[Principle of the useful field of view and normative data].](/assets/img/hold.png)
