Ergonomics
ISSN: 0014-0139 (Print) 1366-5847 (Online) Journal homepage: http://www.tandfonline.com/loi/terg20
Discriminability of Large Weights N. K. CARLSON , C. G. DRUKY & J. A. WEBBER To cite this article: N. K. CARLSON , C. G. DRUKY & J. A. WEBBER (1977) Discriminability of Large Weights, Ergonomics, 20:1, 87-90, DOI: 10.1080/00140137708931603 To link to this article: http://dx.doi.org/10.1080/00140137708931603
Published online: 27 Apr 2007.
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Citing articles: 9 View citing 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: 16 November 2015, At: 20:53
ERGONOMICS, 1977, VOL. 20, NO.1, 87-90
Discriminability of Large Weights By N. K. CARLSON, C. G. DRURY, and J. A. WEBBER Deportment of Industrial Enginooring State Univorsity of New York at Buffalo Buffalo, New YOI'll:
Tho psychophysical mothod of constants was used to measure tho difference limen for lifted weight.s in the range of weights 10-20 kg. This rnngo is nonror to weights used in materials hnndling tasks.
A constuut 'VoLor Fraction of about 0·04 was
Downloaded by [Nanyang Technological University] at 20:53 16 November 2015
found in contrast to the findings of about 0·08 at weights below 3 kg.
1. Introduction The measurement of human ability to cliscriminato between lifted weights has a long history, going back to Fechner (1860). For weights ranging from a few grams to 3·0 kg the traditional finding is a Difference Limen between 6% and 10% of the weight of the standard stimulus (Woodworth and Schlosberg 10(,5 (p. 24). Individual studies show that the Weber Fraction decreases with Increasing stimulus weight although usually remaining in the 6% to 10% range noted above. A review of the recent literature on lifted weight discrimination showed that most current studies are aimed either at refinements of experimental methodology, e.q. John (1972) or at model builcling, e.q. Ross and DiLollo (1970), Anderson and Jacobson (1968). Despite the current interest in safety in manual materials handling (Herrin, Chaffin and Mach 1975, Brown 1972, Drury and Pfeil 1(75) the authors have been unable to locate studies of disoriminability in the range usually associated with materials handling studies (10-40 kg). The study reported in this noto is a simple extension of the data on Weber's Fraction for lifted weights into the' materials handling' range. 1.1. 111ethod.
A pilot study, using five student subjects, was designed on the basis of an expected 7 % 'Weber Fraction. The method of constant stimulli was used with comparison weights approximately - 14 %, - 7%,0, + 7 % and + 14 % different from the standard. Two standards were used-one in the 'usual' range, 0·1064 kg, and one in .the ' materials handling' range, 13·63 kg. The smaller weights were small glass bottles weighted with gravel whilst the larger ones were compact boxes (215 x 425 x 3!l5 mm. high) with handles centered on the lid. Each comparison weight was lifted 10 times in random order. The mean probabilities of judging the comparison stimulus heavier than the standard are in Table 1. It can be seen that for the large weights only two comparisons failed to give perfect disoriminability. The Weber Fraction for the small weights was 7·5% as expected but that for the large weight, calculated on the basis of two points only, was surprisingly low at 4,0%. On the basis of this pilot study, a main experiment was designed on the assumption that the Weber Fraction was in the neighborhood of 4%. Three standard weights of 10 kg, 15 kg, and 20 kg were used. For each standard, five comparison weights were constructed, cliffering from the standard by -5%, -2~%, 0, +2t%, and +5% of standard weight. The weights ERG.
G
N. E. Carlson et al.
88
were made by sand weighting of the same compact boxes used in the pilot study. Six student subjects, all males aged 20-30 y, performed the experiment using each set of weights on a different day. On each day the subject lifted the standard a few centimeters off the gound followed by a comparison stimulus and judged the latter as heavier or lighter than the standard. Each comparison was judged in this way twenty times by each subject in a random order. For the two larger weights the session was run over two days to avoid excessive strain on the subjects. Subjects received each treatment condition in a random order. Downloaded by [Nanyang Technological University] at 20:53 16 November 2015
Tltblo I:
Results of Pilot Study.
0·1064 kg standard
comparison
0·0922
% heavier
IG%
0·0993 25%
0·1064 70%
0·1135 85%
0·1026 100%
13·64 kg standard
comparison % heavier
11-82 0%
12·73 25%
13·64 85%
14-55
100%
15·45 100%
1.2. Rcsnlts
The probabilities of judging heavier by each subject for each standard and comparison were used to calculate a difference limen for each subject and standard combination. A least squares technique was used (Guilford 1954-) tu give a difference limen as a percentage of standard. An analysis of vari(mce on these val ues (Tnblo 2) showed no significant effects of either subjects or standards when tested against their interaction, the only measure of error vurinnco. Plots of the normalized probabilities for each standard arc shown in Figure 1 together with the fitted regression lines, using unweighted values ·2.0
i ~ !e.
.. 1.0
u,
0
...« sw w
0
~
-c
" 0:
0
0 Z
-1.0
, 10.0
11.0
i 14.0
16.0
fr
I
19.0
21.0
COMPARISON WEIGHT, kg
Figure 1:
Psychophysical Functions for Throo Standards, main experiment.
89
Discriminability of Large Weights Table 2:
Analysis of Variance of Weber Fractions, main experiment. 8.8.
d.f.
m.s.a.
F·ratio
Between standards (St) Hot-ween subjects (8) StxS [error}
O'Oi 0·0:' 0·29
2 5 10
0·035 0·01 0·029
< 1·0
TOTAL
0·41
Ii
Downloaded by [Nanyang Technological University] at 20:53 16 November 2015
Source of Variance
1'20
for simplicity. The difference Iimons for each weight were 5·2 %, 3·4%, and 4·3% for the three standard weights. Figure 2 shows and extension of Woodworth and Schlosberg's graph (p. 224) to incorporate tho results of the pilot study and this experiment. It can be seen that beyond ;{ kg the Weber Fraction is consistently lower, in the range :3~% to 5}% confirming the results of the pilot study.
KEY
ISSN: 0014-0139 (Print) 1366-5847 (Online) Journal homepage: http://www.tandfonline.com/loi/terg20
Discriminability of Large Weights N. K. CARLSON , C. G. DRUKY & J. A. WEBBER To cite this article: N. K. CARLSON , C. G. DRUKY & J. A. WEBBER (1977) Discriminability of Large Weights, Ergonomics, 20:1, 87-90, DOI: 10.1080/00140137708931603 To link to this article: http://dx.doi.org/10.1080/00140137708931603
Published online: 27 Apr 2007.
Submit your article to this journal
Article views: 14
View related articles
Citing articles: 9 View citing 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: 16 November 2015, At: 20:53
ERGONOMICS, 1977, VOL. 20, NO.1, 87-90
Discriminability of Large Weights By N. K. CARLSON, C. G. DRURY, and J. A. WEBBER Deportment of Industrial Enginooring State Univorsity of New York at Buffalo Buffalo, New YOI'll:
Tho psychophysical mothod of constants was used to measure tho difference limen for lifted weight.s in the range of weights 10-20 kg. This rnngo is nonror to weights used in materials hnndling tasks.
A constuut 'VoLor Fraction of about 0·04 was
Downloaded by [Nanyang Technological University] at 20:53 16 November 2015
found in contrast to the findings of about 0·08 at weights below 3 kg.
1. Introduction The measurement of human ability to cliscriminato between lifted weights has a long history, going back to Fechner (1860). For weights ranging from a few grams to 3·0 kg the traditional finding is a Difference Limen between 6% and 10% of the weight of the standard stimulus (Woodworth and Schlosberg 10(,5 (p. 24). Individual studies show that the Weber Fraction decreases with Increasing stimulus weight although usually remaining in the 6% to 10% range noted above. A review of the recent literature on lifted weight discrimination showed that most current studies are aimed either at refinements of experimental methodology, e.q. John (1972) or at model builcling, e.q. Ross and DiLollo (1970), Anderson and Jacobson (1968). Despite the current interest in safety in manual materials handling (Herrin, Chaffin and Mach 1975, Brown 1972, Drury and Pfeil 1(75) the authors have been unable to locate studies of disoriminability in the range usually associated with materials handling studies (10-40 kg). The study reported in this noto is a simple extension of the data on Weber's Fraction for lifted weights into the' materials handling' range. 1.1. 111ethod.
A pilot study, using five student subjects, was designed on the basis of an expected 7 % 'Weber Fraction. The method of constant stimulli was used with comparison weights approximately - 14 %, - 7%,0, + 7 % and + 14 % different from the standard. Two standards were used-one in the 'usual' range, 0·1064 kg, and one in .the ' materials handling' range, 13·63 kg. The smaller weights were small glass bottles weighted with gravel whilst the larger ones were compact boxes (215 x 425 x 3!l5 mm. high) with handles centered on the lid. Each comparison weight was lifted 10 times in random order. The mean probabilities of judging the comparison stimulus heavier than the standard are in Table 1. It can be seen that for the large weights only two comparisons failed to give perfect disoriminability. The Weber Fraction for the small weights was 7·5% as expected but that for the large weight, calculated on the basis of two points only, was surprisingly low at 4,0%. On the basis of this pilot study, a main experiment was designed on the assumption that the Weber Fraction was in the neighborhood of 4%. Three standard weights of 10 kg, 15 kg, and 20 kg were used. For each standard, five comparison weights were constructed, cliffering from the standard by -5%, -2~%, 0, +2t%, and +5% of standard weight. The weights ERG.
G
N. E. Carlson et al.
88
were made by sand weighting of the same compact boxes used in the pilot study. Six student subjects, all males aged 20-30 y, performed the experiment using each set of weights on a different day. On each day the subject lifted the standard a few centimeters off the gound followed by a comparison stimulus and judged the latter as heavier or lighter than the standard. Each comparison was judged in this way twenty times by each subject in a random order. For the two larger weights the session was run over two days to avoid excessive strain on the subjects. Subjects received each treatment condition in a random order. Downloaded by [Nanyang Technological University] at 20:53 16 November 2015
Tltblo I:
Results of Pilot Study.
0·1064 kg standard
comparison
0·0922
% heavier
IG%
0·0993 25%
0·1064 70%
0·1135 85%
0·1026 100%
13·64 kg standard
comparison % heavier
11-82 0%
12·73 25%
13·64 85%
14-55
100%
15·45 100%
1.2. Rcsnlts
The probabilities of judging heavier by each subject for each standard and comparison were used to calculate a difference limen for each subject and standard combination. A least squares technique was used (Guilford 1954-) tu give a difference limen as a percentage of standard. An analysis of vari(mce on these val ues (Tnblo 2) showed no significant effects of either subjects or standards when tested against their interaction, the only measure of error vurinnco. Plots of the normalized probabilities for each standard arc shown in Figure 1 together with the fitted regression lines, using unweighted values ·2.0
i ~ !e.
.. 1.0
u,
0
...« sw w
0
~
-c
" 0:
0
0 Z
-1.0
, 10.0
11.0
i 14.0
16.0
fr
I
19.0
21.0
COMPARISON WEIGHT, kg
Figure 1:
Psychophysical Functions for Throo Standards, main experiment.
89
Discriminability of Large Weights Table 2:
Analysis of Variance of Weber Fractions, main experiment. 8.8.
d.f.
m.s.a.
F·ratio
Between standards (St) Hot-ween subjects (8) StxS [error}
O'Oi 0·0:' 0·29
2 5 10
0·035 0·01 0·029
< 1·0
TOTAL
0·41
Ii
Downloaded by [Nanyang Technological University] at 20:53 16 November 2015
Source of Variance
1'20
for simplicity. The difference Iimons for each weight were 5·2 %, 3·4%, and 4·3% for the three standard weights. Figure 2 shows and extension of Woodworth and Schlosberg's graph (p. 224) to incorporate tho results of the pilot study and this experiment. It can be seen that beyond ;{ kg the Weber Fraction is consistently lower, in the range :3~% to 5}% confirming the results of the pilot study.
KEY
