age-differentiated analysis of the hand proximity effect ... · this study, the effect of proximal...

Proceedings 19th Triennial Congress of the IEA, Melbourne 9-14 August 2015

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Age-differentiated analysis of the hand proximity effect in a visual search paradigm

C. Bröhl, S. Antons, J. Bützler, C.M. Schlick

Chair and Institute of Industrial Engineering and Ergonomics of RWTH Aachen University

Bergdriesch 27, 52062 Aachen, GERMANY

A growing literature has suggested that visual information surrounding the hand is viewed and processed differently from information further away. Specifically, there is a tendency to process information near the hand more precisely and this effect can be facilitative or detaining depending on task context. In this study, the effect of proximal hands was studied using an extensive visual search paradigm consisting of alphanumerical characters presented on a screen and organized in a matrix. Therefore, the hands were placed in varying positions: directly at the screen, on the table and on the lap. Furthermore, results were analyzed for hands-near parts of the screen and hands-far parts. As performance in information processing is highly dependent on subject’s age, effects were analyzed age-differentiated. Results show a significant effect regarding hand positions depending on age. Search times were significantly longer for the position of the hand at the screen and for hands-near parts of the screen in the younger age group but not in the older group. Practitioner Summary: Visual information surrounding the hand is viewed and processed differently from information further away and the direction of this effect is highly dependent on task context. In this study, the effect of proximal hands was analyzed using an extensive visual search paradigm and by means of three different hand positions: hands on the screen, hands on the table and hands on the lap. Results were analyzed with regard to search times for different parts of the screen and for two different age groups. Keywords: hand proximity, nearby hands, ergonomic design, age-robust design, visual search

1 Introduction

While interacting with information the source of input has an influence on human perception. Reading on paper is sometimes felt to be more comfortable than on screen. Recent studies have suggested that the location of the hand directs attention to regions near the body. This effect may be explained by the fact that objects near the body, especially the hands, may be candidates for manipulation in potential actions and therefore should be perceived differently. Research focusing on the perception of stimuli near the hands found out that the direction and strength of the effect is mainly dependent on task context, resulting in a positive effect in some tasks, while in other tasks the effect might change to a negative outcome. With regard to visual working memory, for example, a positive effect was found, as more elements could be kept in mind when the hands were near a stimulus. Another positive effect exists when processing of visual stimuli with regard to the detection of a target is required. The results of five experiments administered by Reed, Grubb, and Steele (2006) showed that subjects detected target items which appeared near the hand in a covert attention paradigm more quickly than targets away from the hand and this effect was also present for non-visual hands where only proprioceptive information about the location of the hand was present. Regarding tasks dealing with specific cognitive mechanisms results show that placing the hands near a stimulus can lead to a preference for focusing on details (Davoli, Brockmole, & Goujon, 2012), a delay in attentional disengagement (Abrams, Davoli, Du, Knapp III, & Paull, 2008) and an enhancement in cognitive control mechanisms (Weidler & Abrams, 2014). The effects caused by hand presence were also analyzed in lesion studies with patients having damages in specific brain areas. In this context, Schendel & Robertson (2004) examined the post-stroke vision loss of a hemianopia patient by performing a detection task experiment in which three different conditions were compared. In the first condition, the patient’s left arm lay on his lap, in the second condition, the left arm was positioned in the left visual field and the stimulus presentation took place within reach of the arm, while in the third condition simply the stimulus presentation was varied in


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distance, namely out of the reach of the arm. The results show that an improvement in the severity of the visual deficit can be noticed in the case the arm of the patient acted in the “blind” field during condition two although the patients’ inability to “see” the stimulus.

In summary, study results demonstrate a preferential processing of visual objects near the hands. But besides the effects just described, engaging to stimuli more fully may also be non-facilitative for tasks requiring the processing of words and sentences. Davoli, Du, Montana, Garverick, & Abrams (2010) let subjects judge the sensibleness of sentences, for example, and found that subjects are slower and less effective when their hands are near a visual display compared to when their hands were on the lap. In line with this result Le Bigot & Jaschinski (2011) found more errors in a letter detection task while subjects read pseudo text when the hands were near a computer screen than when the hands were further away from the screen on a desk.

Next to the distance between stimulus presentation and hand position the way how tasks are processed has an influence on the strength of the effect. Most of the studies analyzed tasks where hands were in a task congruent position. Brown, Morrissey and Goodale (2009) however, studied a setting where the palm of the hand was rotated in the direction of the display and compared this position to a setting where the hand was rotated away from the display. What the authors found was a stronger effect of hand proximity when the hand was in a task congruent position, namely rotated with the palm in direction of the display. In another study Festman, Adam, Pratt, & Fischer (2013) studied the effect of hand proximity with moving hands. In grasping movements and pointing tasks a meaningful movement would be in the direction of the stimulus which needs to be attended to. So the authors studied this movement direction and compared it to a movement which went into the opposite way. Their results showed a stronger effect for movements into the direction of the stimulus and this was also true when the hands were not visible but covered under a table. Reed, Betz, Garza, & Roberts (2010) added a tool, specifically a rake, into their study setting and placed this tool in a meaningful position according to the original context of usage in the first condition and in an incongruent position in the second condition. This study again showed a stronger effect for the condition with the tool being in a task congruent condition. What these studies show is the fact that the effect which is engendered through the proximity of the hand is not only originated through the presence of the hand or the tool but also through the functional relation of the hand or the tool to task context.

Evidence for the effect comes from Rizzolatti, Matelli, & Pavesi (1983) and their contribution to the bimodal neuron hypothesis. These researchers studied monkeys with lesions in specific brain regions and found partially separate neural circuits for differing distances around the body. Monkeys with lesions in the unilateral frontal lobe were not able to detect stimuli which were in their reaching distance and monkeys with unilateral lesions in the parietal lobe failed to attend to stimuli beyond reaching distance. Besides these neural systems there are bimodal neurons responding to both visual stimuli which are in the space immediately surrounding the body, called peripersonal space, and tactile information. As the hand moves the receptive fields of the neurons in the brain move with the hand (Gross, Bender, & Rocha-Miranda, 1969). As the effect of proximal hands is stronger for task congruent hand positions and movements it is not caused solely by a difference in attentional engagement to stimuli in peripersonal space but in a change in the process of object perception (Cosman & Vecera, 2010).

Based on these findings, the study described in this paper aims at analyzing the effect evoked by hand presence in a visual search tasks. Therefore, a computer task where subjects had to search for 48 alphanumerical characters organized in a matrix was generated and executed by means of varying hand positions. First, subject’s performance in the visual search task was studied for the hands positioned directly at the screen, on the table and on the lap. Next, results were analyzed for three different parts of the screen separately (two outer parts and one central part). When there is an effect of hand presence this effect should be stronger for the outer parts of the screen near the hands than for the central part. Studies about human-computer interaction have shown that there are profound dissimilarities in performance for separate age groups (e.g. Arning & Ziefle, 2007; Bützler, Bromme, Bröhl, Jochems & Schlick, 2014 Charness, Holley, Feddon, & Jastrzembski, 2004; Grahame, Laberge, & Scialfa, 2004). Prior studies about the influence of age on movement tasks found differences in hand motion that were not attributable to deficits in motor skills but to differences in the perception about peripersonal space (Bloesch, Davoli, & Abrams, 2013). Based on studies administered by Tipper, Lortie, & Baylis (1992) which found that while executing grasping movements the position of the object is automatically encoded in reference to the hand in younger subjects, Bloesch et al. (2013) could show that for older subjects the reference frame is not specifically attributed to


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the hand but the body as a whole. Therefore, results of the study described in this paper are evaluated age-differentiated. 2 Method

2.1 Participants

Altogether 57 right-handed subjects participated in the study with normal or corrected-to-normal vision and gave their informed consent to take part in the study. Subjects were divided in two age groups. In the younger age group age ranged from 20 to 38 years (mean=26.29, SD=4.73) and from 40 to 74 in the older age group (mean=55.05, SD=11.36). All participants had experience with touch technologies either in form of a tablet PC or a smartphone. 2.2 Procedure

Subjects were seated in front of a computer desk with a viewing distance to the monitor of 500 mm. The three hand conditions are shown in figure 1. In each condition a computer mouse which was located under the right hand served as input device. In the first condition both hands were placed at the sides of the display and the arms were supported by an elbow-rest. In the second condition the hands were located at the border of the table and in the third condition the hands were placed on a wooden bar located on the lap. In all three conditions the horizontal distance between the hands was kept constant.

The search display consisted of a matrix containing 48 rectangles with different alphanumerical characters. Characters which look similar in upper and lower case were presented only once. Overall, each of the 48 rectangles needed to be searched for every position of the hands in a random order to make sure that every part of the display is included in the task resulting in 3x48 trials of the visual search task. During every trial one character which needed to be searched was presented first. After that a blank screen was shown as masking stimulus for three seconds and was followed by the search matrix in which alphanumerical characters were arranged randomly in every trial. At the beginning an instruction of the task was given and five practice trials were carried out per condition. Search times were recorded via a mouse click with the right index finger.

Figure 1. Visualization of the study conditions: hands on the screen (left), hands on the table (center) and hands on the lap (right)

2.3 Analysis

To analyze the hands-near and hands-far parts of the screen, the screen was divided in three parts, two outer parts (figure 2, parts 1 and 3) and one central part (figure 2, part 2). In order to analyze the data of the study statistically, repeated measures ANOVA was used with hand position and part of the screen as independent variable and search time as dependent variable. As the two age groups varied in the amount of participants, effects of the groups were analyzed separately. In case Mauchly’s test of sphericity showed a


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significant effect, within-subject effects were analyzed by means of the values corrected by Greenhouse-Geisser. The level of significance was set to α = 0.05 and post-hoc tests were performed using Bonferroni correction.

Figure 2. Depiction of the parts of the screen that were used for the analysis of the hands-near (part 1 and 3) and hands-far screen parts (part 2)

3 Results

As shown in the error bars in figure 3 which represent the 95% confidence interval, older subjects needed more time to execute the tasks. With regard to the three different hand positions the analysis of the two-way ANOVA showed a significant effect in the younger age group (F(2,68)=6.31, p<0.001) but not in the older age group (F(2,42)=.67, p=.94). The Bonferroni post-hoc tests revealed significant differences between the position of the hands at the screen and the hands on the table (p=.05) and between the hands on the screen and the hands on the lap (p<0.001).

Figure 3. Error bar graphs of the search times showing the 95% confidence interval


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Regarding the analysis of the different parts of the screen a significant effect was found for the younger age group (F(2,68)=10.54, p<0.001) but not for the older age group (F(1.46,30.7)=3.15, p=.07). The Bonferroni post-hoc tests revealed significant differences between part 1 and 2 (p=.01) and for part 2 and 3 (p<0.001). Figure 4 shows the 95% confidence intervals of the corresponding values.

Figure 4. Error bar graphs of the parts of the screen showing the 95% confidence interval

Between the factors hand position and screen part there was a significant interaction effect

(F(4,136)=5.14, p=.001). As is depicted in figure 5 the interaction effect can be classified as being disordinal. Interestingly, although post-hoc analysis revealed, that there is an effect between the positions of the hands on the screen and on the table, the direction of the effect is not the same for every position of screen parts but is in the opposite direction for the central part of the screen in comparison to the outer parts. With regards to the significant effect between the position of the hands at the screen and on the lap found by post-hoc analysis the figure shows that the effect is valid and interpretable.

Figure 5. Line graphs of the interaction effect between hand position and part of the screen

4 Discussion

Overall, a significant effect was found for the different hand positions for younger subjects, showing longer search times for positions of the hands at the screen in comparison to positions of the hands on the table and on the lap. Results further show that the effect is declining the farther away the hands are from the


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stimulus. For older aged subjects no significant effect was found which is in line with current literature (see Bloesch et al., 2013) but was not studied with regard to the hand proximity effect so far.

Concerning the analysis of the different parts of the screen in the younger age group, results showed shorter search times for stimuli presented in the middle of the screen in comparison to the outer parts and this effect was found for all of the three hand positions. An explanation, next to hand presence, might be the fact that people tend to search in central parts of a display first, before they go on with the outer parts. However, the significant interaction effect as depicted in figure 5 shows that the effect of shorter search times in central screen parts is more pronounced for the condition where the hands are at the screen in comparison to the conditions where the hands are on the table and on the lap. This indicates that there is an effect of hand presence which also holds although there is a central tendency with regard to tasks dealing with visual search. Regarding effects for the left and right screen part, results reveal that search times are longer for the right part. As only right-handed subjects were studied this could imply that there is more task interference by the prominent hand.

Based on the results of the study, the effect evoked by proximal hands should be analyzed in a second study while subjects are working with a touchscreen. Therefore, the visual search tasks should be used again but instead of responding via mouse the response should be made via a pointing movement on the corresponding character. To make the results comparable to the study described in this paper the time required to make the pointing movement should be calculated via Fitts’ law and subtracted from the overall search time. Furthermore, eye-tracking measures should be used to study the effect. Especially the mean fixation duration, which is an indicator for the difficulty to extract information from a display, and the pupil dilation, which can indicate cognitive workload, will be examined.

Acknowledgements The research was funded by the German Research Foundation according to the transfer project (SCHL 1805/6-1). References

Abrams, R. A., Davoli, C. C., Du, F., Knapp III, W. H., & Paull, D. 2008. "Altered vision near the hands". In Cognition, 107(3), 1035–1047.

Arning, K., & Ziefle, M. 2007. "Understanding age differences in PDA acceptance and performance". In Computers in Human Behavior, 23(6), 2904–2927.

Bloesch, E. K., Davoli, C. C., & Abrams, R. A. 2013. "Age-Related Changes in Attentional Reference Frames for Peripersonal Space". In Psychological Science, 0956797612457385.

Brown, L. E., Morrissey, B. F., & Goodale, M. A. 2009. "Vision in the palm of your hand". In Neuropsychologia, 47(6), 1621–1626.

Bützler, J. 2014. "Layout Structures of Network Diagrams in Projects Project Management Software: An Age-Differentiated Empirical Investigation Concerning Symmetry and Space" In: Proceedings of the 5th International Conference on Applied Human Factors and Ergonomics 2014 (AHFE), Hrsg.: Ahram, T.; Karwowski, W.; Marek, T., , Stoughton, FL, USA 2014, p. 368-379.

Charness, N., Holley, P., Feddon, J., & Jastrzembski, T. 2004. "Light Pen Use and Practice Minimize Age and Hand Performance Differences in Pointing Tasks". In Human Factors: The Journal of the Human Factors and Ergonomics Society, 46(3).

Cosman, J. D., & Vecera, S. P. 2010. "Attention affects visual perceptual processing near the hand". In Psychological Science.

Davoli, C. C., Brockmole, J. R., & Goujon, A. 2012. "A bias to detail: how hand position modulates visual learning and visual memory". In Memory & Cognition, 40(3), 352–359.

Davoli, C. C., Du, F., Montana, J., Garverick, S., & Abrams, R. A. 2010. "When meaning matters, look but don’t touch: The effects of posture on reading". In Memory & Cognition, 38(5), 555–562.

Festman, Y., Adam, J. J., Pratt, J., & Fischer, M. H. 2013. "Continuous hand movement induces a far-hand bias in attentional priority". In Attention, Perception, & Psychophysics, 75(4), 644–649.

Grahame, M., Laberge, J., & Scialfa, C. T. 2004. "Age Differences in Search of Web Pages: The Effects of Link Size, Link Number, and Clutter". In Human Factors: The Journal of the Human Factors and Ergonomics Society, 46(3), 385–398.


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Gross, C. G., Bender, D. B., & Rocha-Miranda, C. E. 1969. "Visual receptive fields of neurons in inferotemporal cortex of the monkey". In Science, 166(910), 1303–1306.

Le Bigot, N., & Jaschinski, W. 2011. "Hand position at computer screens: effect on visual processing" (pp. 85–88). ACM.

Reed, C. L., Betz, R., Garza, J. P., & Roberts, R. J. 2010. "Grab it! Biased attention in functional hand and tool space". In Attention, Perception, & Psychophysics, 72(1), 236–245.

Reed, C. L., Grubb, J. D., & Steele, C. 2006. "Hands up: Attentional prioritization of space near the hand". In Journal of Experimental Psychology: Human Perception and Performance, 32(1), 166–177.

Rizzolatti, G., Matelli, M., & Pavesi, G. 1983. "Deficits in attention and movement following the removal of postarcuate (area 6) and prearcuate (area 8) cortex in macaque monkeys". In Brain, 106(3), 655–673.

Schendel, K., & Robertson, L. C. 2004. "Reaching out to see: Arm position can attenuate human visual loss". In Journal of Cognitive Neuroscience, 16(6), 935–943.

Tipper, S. P., Lortie, C., & Baylis, G. C. 1992. "Selective reaching: Evidence for action-centered attention". In Journal of Experimental Psychology: Human Perception and Performance, 18(4), 891–905.

Weidler, B. J., & Abrams, R. A. 2014. "Enhanced cognitive control near the hands". In Psychonomic Bulletin & Review, 21(2), 462–469.

age-differentiated analysis of the hand proximity effect ... · this study, the effect of proximal...

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