Role of handedness in flying performance

Material and Methods

A total of 20 healthy male individuals in the age group of 20-39 yrs (30±4 yrs) volunteered for the study. Based on their self-reported handedness and being either a pilot (P) or a non-pilot (NP), they were placed in four groups; right-handed pilots, right-handed non-pilots, left-handed pilots and left-handed non-pilots. Each group had five subjects. The pilots were both, military and civil aviators with more than 450 hrs of flying experience. None of the volunteers had any compromise in their cognitive and motor performance. All had a fair knowledge and proficiency in operating computers.

Results

The PMT scores of the Two-hand Coordination test for the four groups are presented in Tables 1.1-1.4 and graphically depicted in Figure 1. The difference in the mean PMT scores between the right-handed and left-handed pilots, and also between the right-handed and left-handed non-pilot groups was not found to be statistically significant. The difference in the mean PMT scores between the left-handed pilots and the left-handed non-pilots and also that between the right-handed pilots and the right-handed non-pilots was not found to be statistically significant (Table 4.1).

The time scores for the Minnesota Rate of Manipulation Test for the four groups are presented in Tables 2.1-2.4 and graphically depicted in Figure 2. The difference in the mean time scores between the right-handed and left-handed pilots, and also between the right-handed and left-handed non-pilot groups was not found to be statistically significant. Moreover, the difference in the mean time scores between the left-handed pilots and the left-handed non-pilots and also that between the right-handed pilots and the right-handed non-pilots was not found to be statistically significant (Table 4.2 and 4.3).

The time scores for Finger Dexterity Test are presented in Tables 3.1-3.4 and graphically depicted in Figure 3. The difference in the mean time scores between the right and left-handed pilots, in the four groups was not found to be statistically significant. The difference in the mean time scores of the same-sided hands between the four groups was not found to be statistically significant (Tables 4.4 and 4.5). The difference of the time scores of the opposite sided hands (i.e. left hand of one group with the right hand of the other group) between the four groups was not found to be statistically significant except for one combination. The difference in the mean time scores of that of the right hand of the left-handed pilot group and the right hand of the right-handed pilot group was significant at p<0.05 (Table 4.4).

Of the 257 pilots surveyed, 19 (7.74%) were left-handed, 237 (92.2 %) were right-handed and 1 (0.4%) was found to be ambidextrous laterality score=0).

3 out of 19 left-handed pilots (17.6%) were highly lateralized (Laterality Quotient -75). Right-handed pilots showed high lateralization (Laterality Quotient +75) in 185 out of 237(88.1%). Conversely, mixed handedness was present in 69 pilots (82.4% of left-handed and 21.9% of the right-handed) (Table 5)

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Figure 1

PMT Ratios of the Subjects in the Two Hand Coordination Test

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Figure 2

Time score of the Subjects for Right Hand in the Minnesota Rate of Manipulation Test

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Figure 3

Time score of the Subjects for Left Hand in the Minnesota Rate of Manipulaticn Test

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Figure 4

Time scores in seconds of the Right-Handed Non-Pilot for Right hand in the Finger Dexterity Test

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Figure 5

Time scores in seconds of the Right-Handed Non-Pilot for Left hand in the Finger Dexterity Test

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Discussion

The Left-handers are in a minority in any population. Living in a world apparently designed for the right-handers, the left-handers are constantly accommodating and learning to cope with the “right-handed” tools and workplaces. For this reason, in the performance of most routine tasks, they perform as well as the right-handers. That they may be facing difficulty in achieving optimum performance, especially in situations requiring high levels of skill, is not apparent. It is not certain whether the left-handers are compromised by their special attribute. This could be as they are few in numbers, and implication of left-handedness as a contributing factor in incidents or accidents is rare. That left-handers are at a disadvantage requires to be demonstrated by controlled studies. Such studies would be based on tests of eye hand coordination in simulated flying environment. In this study, performance of left and right-handers was assessed using a Psychomotor Rig having controls for both hands and also by using two standard tests for manual dexterity.

The Psychomotor Rig presents controls akin to that present in a conventional cockpit. The scores of this test are related to the degree of coordination achieved by the subject, in the use of both hands simultaneously, in the execution of a task. The mean scores achieved by the lefthanders were as good as that achieved by the right-handers. This was against the expectation that left-handed individuals would score significantly lower than the right-handed. This implied that in the two-hand coordination task there was no compromise because of handedness of the subject. These findings were in agreement with Leon [4] who had reported that movements in one limb were not affected by actions in the other limb. It may be for similar reasons that in multi-crew cockpits of transport and passenger aircraft, pilots have not reported any difficulty in operating controls at either the left or right seat even though the layout of the controls is a “mirror image”.

MRMT was a test of eye-hand and arm-hand coordination. It consisted of a primary task carried out by the hand under test and a secondary task assisted by the other hand. Though performed by both hands, the time score was attributed to the hand carrying out the primary task. The time score was inversely related to the performance. It was expected that the performance scores with the dominant hand would be higher than that with the non-dominant hand. This was not found in this study. It was also expected that the left (dominant) hand of the left-hander would be equal in performance to the right (dominant) hand of the right-hander. This was found to be so. The time scores achieved by the left hand were marginally different from that scored by the right hand in all four groups. These differences were not statistically significant. This led to the inference that there is no difference between the dominant and non-dominant hands in performance of tasks requiring eye-hand and arm-hand coordination. It was also revealed that amongst the right-handed, the scores obtained by the left hand (non-dominant) were slightly better than that obtained by the right (dominant) hand in both pilots and non-pilots. In contrast, amongst the left-handers, in both the pilots and non-pilots, this trend was not present. This variation is not taken into consideration, as it is not statistically significant. Inconsistencies in performance with left hand in left-handers have been reported earlier [5, 6]. It was also found that in right-handers the non-dominant was consistently better. The findings in this study are in agreement with studies in past.

The Finger Dexterity Test is used to assess a subject’s fine motor skills. It is performed by one hand and the time score is inversely related to the performance. This test revealed that there was no statistically significant difference between the performance scores of the left and right hands in any of the groups. The results of this study differ with the findings of study done in 2001 that the non right-handers were faster than the right-handers [7], Comparison across the groups revealed significant difference in only one case. The performance by the dominant (right) hand of right-handed pilots was better than non-dominant (right) hand of left-handed pilots. The difference was significant at p< 0.05. This was as expected. Precision of movement is important in the successful execution of fine motor skill. Such a skill is a requisite in the performance of actions related to operate the trim control or switches, which though not directly related to the handling of the primary controls of the aircraft, is still an important part of flying.

The handedness survey covered a total of 257 pilots and found that 19 (7.4 %) were left-handed. This incidence of 7.4 % was within the stated incidence for left-handed individuals in general population. The laterality quotient scores in the survey also revealed the spectrum of laterality. Of the 19 left-handed, 3 were highly lateralized and of the 237 right-handed, 185 were highly lateralized. 69 (26.8 %) pilots were mixed-handed. The relative incidence revealed that 82.4% of the left-handed and 21.9% of the right-handed were mixed-handed. The survey also revealed that the score of only one person was such that he could be considered as ambidextrous. Similar incidence of left-handedness in the general population, and also in the pilot population, lead to the inference that there is no bias in the flying environment against left-handers. Apparently the selection process and the flying training do not discriminate against the left-handers.

The analysis of the laterality quotient gives interesting results. 16 of the 19 left-handers had varying degrees of mixed handedness while only 52 out of the 237 right-handers had this trait. Percentage wise, this trait of being less lateralized was remarkably higher in the left-handers (84.2 % vs 21.9 %); a finding similar to the one reported by Crowley [8]. This may be because the lefthanders learn to use their non-dominant hand while living in the world “apparently designed for the right-hander.” It also leads us to think that nature endows the left-handers with mixed handedness as 84.2 % of them were in this category. Studies have probed whether mixed handedness is a natural trait or is acquired [9], Same study stated that the incidence of left-handedness decreases with age and has implied that the left-handers learn to acquire skills with their right hands as part of the process of growing up. That the left-handers learn to use the non-dominant more than the right-handers is evident from the relative percentages of incidence (82.4 % in left-handers vs. 21.9 % in the right-handed). This may explain why the left-handed do as well as their right-handed counterparts in all fields including flying as the incidence of left-handers in the sampled pilots was found to be no different from that of the general population. This is in consonance with the findings of earlier studies on the impact of handedness on flying training, and no bias against the left-handers was found [1],

Conclusion

In this study the hand dexterity was assessed in Right and Left-Handed aircrew and non-aircrew using laboratory models. The non-aircrew were included to represent the normal population. The results revealed that in two-hand coordination and eye-hand coordination tasks and also in hand dexterity tasks the left-handed aircrew was not at a disadvantage. This favored the view that there was no bias against left-handers in the conventional cockpit. The handedness survey revealed that the incidence of the left-handers in aviators was the same as that in the general population strengthening the view that there is no bias against the left-hander in flying selection or training. A spectrum of laterality was observed and the relative incidence of mixed handedness was found to be more in the left-handed.