Ergonomics
ISSN: 0014-0139 (Print) 1366-5847 (Online) Journal homepage: http://www.tandfonline.com/loi/terg20
An investigation of behaviour changes of subjects learning manual tasks HAIM GERSHONI To cite this article: HAIM GERSHONI (1979) An investigation of behaviour changes of subjects learning manual tasks, Ergonomics, 22:11, 1195-1205, DOI: 10.1080/00140137908924694 To link to this article: http://dx.doi.org/10.1080/00140137908924694
Published online: 24 Oct 2007.
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Article views: 10
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Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=terg20 Download by: [Nanyang Technological University]
Date: 12 November 2015, At: 09:03
ERGONOMICS,
1979, VOL. 22, NO. 11, 1195-1206
An investigation of behaviour changes of subjects learning manual tasks By HAIM
GERSHONI
Downloaded by [Nanyang Technological University] at 09:03 12 November 2015
Technion-Israel Institute of Technology, Technion City, Haifa, Israel
In an effort to determine how behaviour changes as new tasks are learned, films were made and analysed- of workers learning a simple task. Frame by frame analysis of these films revealed that the distance of moves might increase or decrease with experience. Velocity for the most part was close to the standard even for novice workers. For positioning movements fumbling seemed to be the major factor, but even at the beginning of the learning period some cycles were performed in the standard time.
1. Introduction When a worker is taught a manual task, the time required to reach the standard output is a matter of serious concern to both the worker and his employer. Numerous aspects oflearning have been studied,' but when one considers this situation, there are many questions still to be answered. The learning curve, such as shown in figure 1 has .been known to industrial engineers for many years (Blackburn 1936, De long 1957). One accepts that a novice worker will normally perform a task with a cycle time far greater than the standard, but his performance will improve with experience. Eventually the cycle time will approach an asymptote near the standard time.
OJ
E
'';::
~
u
CJ ~""./ ""'./..1..,1."" '-'.I..1../.kI~(..I../-':';~~T.:J.~
fi~~dard
Cycles performed
Figure 1. Traditional learning curve.
Knowing that the cycle time will progress as shown by the learning curve one might well ask, 'how does the worker's behaviour change during the learning process?'. This is the heart of the matter for, if one understands the behavioural changes that occur, it may well be possible to assist the novice in reaching the standard output in a shorter time. In this research attempts were made to see how behaviour changed during the learning process or, in other words, what was the worker really learning to do? Hilgard (1956) suggested that the common name 'learning' can have somewhat different meanings such as: acquisition of a motor skill, memorization of a poem, solving a geometrical puzzle, or understanding a period of history. Furthermore, the explanation of one type of learning may not apply to another. Thus it is important to define one's interpretation of the term.
Downloaded by [Nanyang Technological University] at 09:03 12 November 2015
1196
H. Gershoni
The type of learmng considered here is that associated with workers performing repetitivemanual tasks where the degree oflearning is expressed by the cycle time. Such tasks are typical of many performed by industrial workers who mechanically complete cycle after cycle without the need for conscious decisions; within a very short period, usually less than 50 cycles, the novice: learns what to do. Following this threshold period, his behaviour becomes automatic and the cycle time decreases with practice (Hancock et al. 1965). Attempts have been made to determine the factors affecting this type of learning, but the picture is still incomplete. Motivation certainly affects the speed with which workers learn (Gershoni 1971), but there obviously are other factors involved. Barnes (1940)suggested that the shaded area offigure 1 is essentially due to needless fumbles. As the worker practices the operation, he learns to work with fewer fumbles and the curve approaches the minimum time. While this explanation describes how complex grasps and positions improve, it does not explain how the worker's behaviour changes while learning other motions. Crossman (1969) suggests that the novice worker selects different motion patterns from a personal repertoire and experiments with these methods until the best technique is found. This explanation might well apply to the threshold period, but it implies that workers always try the worst method first. Crossman also points out that since the worker may not have sufficient feedback to indicate success or failure ofa method, there may be other factors at work. It is important to note that these approaches to the problem evaluated progress by the average cycle time and by the changes in the distributions of the cycle time. However, with the development of predetermined motion time systems such as MTM (Methods Time Measurement), it is possible to use a much finer measure ofprogress in learning. With such techniques qualified analysts can list the motions required to carry out a given task and, by assigning standard times to each motion, determine the standard cycle time (Maynard et al. 1948). One would define a work method as described in terms of such individual motions as the Micro-Method. Hancock et al. (1965) establishedlearning curves for the various motions used in MTM analyses and this again leads us back to the original question. It would appear that the time to complete each motion of a complex task improves with practice, but how does the behaviour change? Less fumbling might explain why grasps and positions improve, but what of reaches and moves where fumbling is not a factor? Does the velocity of such motions increase with time, or are there other factors at work? The following experiments were an attempt to understand this aspect of manual learning. 2. Method Movie films were made of a sample of workers learning a simple manual task. The films were later analysed to detect changes in behaviour as learning progressed. 2.1. The task
Twenty marbles were loaded into the delivery tube shown in figure 2 (Arnon 1972). Due to the slight incline of the tube the marbles automatically rolled to the pickup point 'A' which was 10cm from a cup. Each worker was asked to move the 20 marbles one at a time with a special tweezer from the pickup point 'A' to the cup as fast as they were able.
An investigation of behaviour changes of subjects learninq manual casks
1197
Path of hand
1--7em-l Cup
Downloaded by [Nanyang Technological University] at 09:03 12 November 2015
P-
1---10 em--! Figure 2. Task layout.
After each trial of 20 marbles, the worker rested a few minutes while the marbles were again loaded into the delivery tube. The procedure was repeated again until each worker had performed five or six trials, or a total of 100 to 120 marbles. (Five trials for each worker were originally planned, but in some cases sufficient film remained for an add itional trial.) To be sure, the 100 or 120 times the worker performed the task could not be considered a substantial learning period, for to complete the learning cycle would require many thousands of cycles (Gershoni 1971). However, it was hoped that these films would reveal insight into the sort ofchanges in behaviour which occur. One might assume that a process of change observed in the first 100 cycles might continue throughout theentire learning process. However, such an assumption would have to be verified in long term tests. The nine workers were a random selection from the staff of the Negev Research Institute in Beer-Sheva. The movies were photographed at 24 frames S-l with a Bolex H /6 /6 mm Cinematograph camera having an electric motor drive. 2.2. Definition of the motions A frame by frame examination of a worker carrying out this task reveals that each cycle consists of essentially three motions: I. Move marble from 'A' to cup. 2. Move tweezer from cup back to pickup point 'A'. 3. Gain control of next marble with tweezer.
However, it is useful to look ahead at the ultimate motion pattern which it is believed the worker will achieve in time and use this as a standard (table I). These motions were defined in the terms ofan MTM analysis. Figure I, however, also includes a description of each motion. The first motion is defined as a move to the general location of the mouth of the cup. The worker could choose the release point as long as the marble reached the cup. The standard distance for the path of the hand, see figure 2, was arbitrarily assumed to be 152mm (6 in). The time was recorded in frames of movie film since in the film analysis the simplest means of noting time was to count the frames. The time of 7·7 frames is the equivalent of the MTM standard time for such a 152mm (6 in) move-M6B. The return motion to grasp the marble requires more precision and was defined in terms of MTM as an M6C with a standard time of 8·9 frames.
1198
H. Gershoni Table I.
Motions used in performing the task. Standard time
MTM notation
in frames
Description
M6B
7·7
2
M6C
8·9
3a
A series of small movements during learning No motion required after
as required
Move marble to cup (release of marble during latter part of move) Move tweezer from cup to pickup point Grasp marble with tweezers
0
Grasp marble with tweezers
Downloaded by [Nanyang Technological University] at 09:03 12 November 2015
Motion
3b
learning
Motion 3 presents a somewhat more complex problem of definition. During the learning period, the worker requires a series of motions to place the tweezers on the marble and to allow him to grasp the marble prior to the move. The number of such moves varies considerably from cycle to cycle. However, in the long run, one might expect that the subject will learn to bring the tweezers to the proper location over the marble during the M6C move. In other words, in time he will be able to place the tweezers without the positioning motions. Moreover, it might further be expected that the tweezers will be closed during this M6C move and the following M6B move to the cup. Hence, in the long run the Grasping Motion would tend to disappear. As will be seen, there is considerable evidence in these tests to su pport such a view. 2.3. A naly/ ical procedure The films analysed with an Land W Motion Anulyzer projector, and in the first :~ phase of the investigation the frames required to carry out each motion of every cycle were coun ted. However, after analysing the performance of several workers, it was noted that the moves were not performed in the same manner by all workers and as learning took place the arc of the moves seemed to change. Thus, it was decided to plot the actual path followed by the hand for each move. This was done by projecting the films life size on tracing paper and marking the ____+-T
+
/
+,
ISSN: 0014-0139 (Print) 1366-5847 (Online) Journal homepage: http://www.tandfonline.com/loi/terg20
An investigation of behaviour changes of subjects learning manual tasks HAIM GERSHONI To cite this article: HAIM GERSHONI (1979) An investigation of behaviour changes of subjects learning manual tasks, Ergonomics, 22:11, 1195-1205, DOI: 10.1080/00140137908924694 To link to this article: http://dx.doi.org/10.1080/00140137908924694
Published online: 24 Oct 2007.
Submit your article to this journal
Article views: 10
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=terg20 Download by: [Nanyang Technological University]
Date: 12 November 2015, At: 09:03
ERGONOMICS,
1979, VOL. 22, NO. 11, 1195-1206
An investigation of behaviour changes of subjects learning manual tasks By HAIM
GERSHONI
Downloaded by [Nanyang Technological University] at 09:03 12 November 2015
Technion-Israel Institute of Technology, Technion City, Haifa, Israel
In an effort to determine how behaviour changes as new tasks are learned, films were made and analysed- of workers learning a simple task. Frame by frame analysis of these films revealed that the distance of moves might increase or decrease with experience. Velocity for the most part was close to the standard even for novice workers. For positioning movements fumbling seemed to be the major factor, but even at the beginning of the learning period some cycles were performed in the standard time.
1. Introduction When a worker is taught a manual task, the time required to reach the standard output is a matter of serious concern to both the worker and his employer. Numerous aspects oflearning have been studied,' but when one considers this situation, there are many questions still to be answered. The learning curve, such as shown in figure 1 has .been known to industrial engineers for many years (Blackburn 1936, De long 1957). One accepts that a novice worker will normally perform a task with a cycle time far greater than the standard, but his performance will improve with experience. Eventually the cycle time will approach an asymptote near the standard time.
OJ
E
'';::
~
u
CJ ~""./ ""'./..1..,1."" '-'.I..1../.kI~(..I../-':';~~T.:J.~
fi~~dard
Cycles performed
Figure 1. Traditional learning curve.
Knowing that the cycle time will progress as shown by the learning curve one might well ask, 'how does the worker's behaviour change during the learning process?'. This is the heart of the matter for, if one understands the behavioural changes that occur, it may well be possible to assist the novice in reaching the standard output in a shorter time. In this research attempts were made to see how behaviour changed during the learning process or, in other words, what was the worker really learning to do? Hilgard (1956) suggested that the common name 'learning' can have somewhat different meanings such as: acquisition of a motor skill, memorization of a poem, solving a geometrical puzzle, or understanding a period of history. Furthermore, the explanation of one type of learning may not apply to another. Thus it is important to define one's interpretation of the term.
Downloaded by [Nanyang Technological University] at 09:03 12 November 2015
1196
H. Gershoni
The type of learmng considered here is that associated with workers performing repetitivemanual tasks where the degree oflearning is expressed by the cycle time. Such tasks are typical of many performed by industrial workers who mechanically complete cycle after cycle without the need for conscious decisions; within a very short period, usually less than 50 cycles, the novice: learns what to do. Following this threshold period, his behaviour becomes automatic and the cycle time decreases with practice (Hancock et al. 1965). Attempts have been made to determine the factors affecting this type of learning, but the picture is still incomplete. Motivation certainly affects the speed with which workers learn (Gershoni 1971), but there obviously are other factors involved. Barnes (1940)suggested that the shaded area offigure 1 is essentially due to needless fumbles. As the worker practices the operation, he learns to work with fewer fumbles and the curve approaches the minimum time. While this explanation describes how complex grasps and positions improve, it does not explain how the worker's behaviour changes while learning other motions. Crossman (1969) suggests that the novice worker selects different motion patterns from a personal repertoire and experiments with these methods until the best technique is found. This explanation might well apply to the threshold period, but it implies that workers always try the worst method first. Crossman also points out that since the worker may not have sufficient feedback to indicate success or failure ofa method, there may be other factors at work. It is important to note that these approaches to the problem evaluated progress by the average cycle time and by the changes in the distributions of the cycle time. However, with the development of predetermined motion time systems such as MTM (Methods Time Measurement), it is possible to use a much finer measure ofprogress in learning. With such techniques qualified analysts can list the motions required to carry out a given task and, by assigning standard times to each motion, determine the standard cycle time (Maynard et al. 1948). One would define a work method as described in terms of such individual motions as the Micro-Method. Hancock et al. (1965) establishedlearning curves for the various motions used in MTM analyses and this again leads us back to the original question. It would appear that the time to complete each motion of a complex task improves with practice, but how does the behaviour change? Less fumbling might explain why grasps and positions improve, but what of reaches and moves where fumbling is not a factor? Does the velocity of such motions increase with time, or are there other factors at work? The following experiments were an attempt to understand this aspect of manual learning. 2. Method Movie films were made of a sample of workers learning a simple manual task. The films were later analysed to detect changes in behaviour as learning progressed. 2.1. The task
Twenty marbles were loaded into the delivery tube shown in figure 2 (Arnon 1972). Due to the slight incline of the tube the marbles automatically rolled to the pickup point 'A' which was 10cm from a cup. Each worker was asked to move the 20 marbles one at a time with a special tweezer from the pickup point 'A' to the cup as fast as they were able.
An investigation of behaviour changes of subjects learninq manual casks
1197
Path of hand
1--7em-l Cup
Downloaded by [Nanyang Technological University] at 09:03 12 November 2015
P-
1---10 em--! Figure 2. Task layout.
After each trial of 20 marbles, the worker rested a few minutes while the marbles were again loaded into the delivery tube. The procedure was repeated again until each worker had performed five or six trials, or a total of 100 to 120 marbles. (Five trials for each worker were originally planned, but in some cases sufficient film remained for an add itional trial.) To be sure, the 100 or 120 times the worker performed the task could not be considered a substantial learning period, for to complete the learning cycle would require many thousands of cycles (Gershoni 1971). However, it was hoped that these films would reveal insight into the sort ofchanges in behaviour which occur. One might assume that a process of change observed in the first 100 cycles might continue throughout theentire learning process. However, such an assumption would have to be verified in long term tests. The nine workers were a random selection from the staff of the Negev Research Institute in Beer-Sheva. The movies were photographed at 24 frames S-l with a Bolex H /6 /6 mm Cinematograph camera having an electric motor drive. 2.2. Definition of the motions A frame by frame examination of a worker carrying out this task reveals that each cycle consists of essentially three motions: I. Move marble from 'A' to cup. 2. Move tweezer from cup back to pickup point 'A'. 3. Gain control of next marble with tweezer.
However, it is useful to look ahead at the ultimate motion pattern which it is believed the worker will achieve in time and use this as a standard (table I). These motions were defined in the terms ofan MTM analysis. Figure I, however, also includes a description of each motion. The first motion is defined as a move to the general location of the mouth of the cup. The worker could choose the release point as long as the marble reached the cup. The standard distance for the path of the hand, see figure 2, was arbitrarily assumed to be 152mm (6 in). The time was recorded in frames of movie film since in the film analysis the simplest means of noting time was to count the frames. The time of 7·7 frames is the equivalent of the MTM standard time for such a 152mm (6 in) move-M6B. The return motion to grasp the marble requires more precision and was defined in terms of MTM as an M6C with a standard time of 8·9 frames.
1198
H. Gershoni Table I.
Motions used in performing the task. Standard time
MTM notation
in frames
Description
M6B
7·7
2
M6C
8·9
3a
A series of small movements during learning No motion required after
as required
Move marble to cup (release of marble during latter part of move) Move tweezer from cup to pickup point Grasp marble with tweezers
0
Grasp marble with tweezers
Downloaded by [Nanyang Technological University] at 09:03 12 November 2015
Motion
3b
learning
Motion 3 presents a somewhat more complex problem of definition. During the learning period, the worker requires a series of motions to place the tweezers on the marble and to allow him to grasp the marble prior to the move. The number of such moves varies considerably from cycle to cycle. However, in the long run, one might expect that the subject will learn to bring the tweezers to the proper location over the marble during the M6C move. In other words, in time he will be able to place the tweezers without the positioning motions. Moreover, it might further be expected that the tweezers will be closed during this M6C move and the following M6B move to the cup. Hence, in the long run the Grasping Motion would tend to disappear. As will be seen, there is considerable evidence in these tests to su pport such a view. 2.3. A naly/ ical procedure The films analysed with an Land W Motion Anulyzer projector, and in the first :~ phase of the investigation the frames required to carry out each motion of every cycle were coun ted. However, after analysing the performance of several workers, it was noted that the moves were not performed in the same manner by all workers and as learning took place the arc of the moves seemed to change. Thus, it was decided to plot the actual path followed by the hand for each move. This was done by projecting the films life size on tracing paper and marking the ____+-T
+
/
+,
