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Were the Victorians cleverer than us? Maybe, maybe not
Intelligence 47 (2014) 1–2
Contents lists available at ScienceDirect
Intelligence
Were the Victorians cleverer than us? Maybe, maybe not Scott Parker ⁎ Department of Psychology, American University, Washington DC 20016-8062, United States
a r t i c l e
i n f o
Article history: Received 6 March 2014 Received in revised form 18 June 2014 Accepted 18 August 2014 Available online xxxx
a b s t r a c t Woodley et al. (2013) noted an increasing trend in reported values of visual reaction times collected over 115 years and concluded that it indicated a decline of intelligence over that period. But because visual reaction times vary with a great many factors in addition to intelligence (notably stimulus luminance) that inference is underdetermined. © 2014 Elsevier Inc. All rights reserved.
Keywords: Dysgenic trend Simple visual reaction time Luminance
Contents
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Woodley, te Nijenhuis, and Murphy (2013) inventoried many studies of visual reaction time (RT) collected between the 1880s and 2004 and found a significant increase of RT over time. Their secular trend line gives trend-weighted mean RTs of about 193 ms in 1889 and about 270 ms in 2004—an increase of about 77 ms in a bit over a century. Because RT is known to be strongly related to intelligence (e.g., Jensen, 2006) the increase of RT over time might indicate that intelligence has declined over the last 120 years or so. However, visual RT is known to vary with many things other than intelligence. Dodonova and Dodonov (2013) discuss many of them. One important family of contributors is the characteristics of the visual stimulus to which the subjects react. Dodonova and Dodonov (2013) discuss many of those, based on a review of that literature by Teichner and Krebs ⁎ Tel.: +1 202 885 1719. E-mail address: [email protected].
http://dx.doi.org/10.1016/j.intell.2014.08.002 0160-2896/© 2014 Elsevier Inc. All rights reserved.
(1972). Prominent among those contributors is the luminance of the stimuli to which the subjects are to react. The idea that increasing stimulus intensity shortens reaction time is an old one. According to Neumann and Niepel (2004), results to that effect were found in the 1860s by Hirsch and the 1870s by Exner. Cattell (1885) reported data showing that trend. And Scripture (1895, p.48) wrote, “The intensity of the light has a very great influence. A very weak light might give 33 [hundredths of a second] while a strong one would give 20 [hundredths of a second] for the same person.” More recent work has confirmed that pattern. For example, Minucci and Connors (1964) showed a decrease of average binocular visual RT of about 60 ms as luminance of a 60-ms flash increased roughly a thousandfold (decrease for the dominant eye alone was about 80 ms and that for the nondominant eye was about 90 ms). Cardello (1979) showed a similar result for 1-second flashes—an average RT reduction of about 75 ms over a thousandfold increase in luminance. For approximately
2
S. Parker / Intelligence 47 (2014) 1–2
hundredfold changes in luminance, the RT reductions were about 35–40 ms in both studies. More extensive data is shown in both Mansfield (1973) and Teichner and Krebs (1972). Thousandfold changes in luminance are not so extreme as they might sound to people unfamiliar with them. A comfortable reading illumination is 1/1000 the luminance of a piece of white paper in sunlight but 1000 times the luminance of that white paper in moonlight. The human visual system is sensitive to an enormous range of luminances; a bright tungsten filament has 1013 times the luminance of a light at absolute threshold. (Riggs, 1966, p.26). Because of the dependence of visual RT on luminance, comparisons across studies of visual RT such as Woodley et al.'s (2013) should consider the luminances of the stimuli used in those studies. Sizeable differences in RT can arise from differences in the stimuli. With that in mind, I looked at the studies that Woodley et al. referred to and found, to my disappointment, that none of those studies specified the luminance of the stimuli. Dodonova and Dodonov (2013) say that we do not know enough about the studies used in Woodley et al. to estimate the variation in RT due to differences in stimulus luminance. Fig. 1 of Woodley et al. (2013) plots mean RT as a function of year for 16 data sets and exhibits a significant correlation between them. Inspection of that figure shows that there is an enormous range of mean RTs (a range of about 90 ms) reported by studies published between 1941 and 1945 and an even larger range (about 140 ms) reported by studies published between 1987 and 2004 (the newest studies used by Woodley et al.) Note that both of these ranges, observed in fairly narrow time periods, exceed the 77-ms shift in mean RT that Woodley et al. estimate to have occurred over the course of the 117 years from 1887 to 2004. Indeed, the observations that are crucial to the Woodley et al. (2013) finding are the earliest ones—those from Galton (as reported in Johnson et al., 1985) and Thompson (1903). Both of those data sets report very short reaction times and contribute greatly to the correlation between RT and year of report. Do those short reaction times betoken a high level of intelligence among the Victorians? In one of those cases, another factor may have contributed. Thompson (1903) generated her stimuli, flashes of purple light, using a Geissler tube—an ancestor of the fluorescent tube (Hick, 1952). But Dunlap and Wells (1910) chose to use a different light stimulus generator, explaining (p.320) that, “A Geissler tube could not be used, on account of the noise accompanying its flash.” Auditory RTs, like visual RTs, grow faster with increasing stimulus intensity (Luce, 1986). We would need to know both the auditory and visual intensities of the Geissler tube to know if Dunlap and Wells's concern was well-founded. But we cannot rule out the possibility that Thompson's subjects were reacting to a noise functionally more intense than the flash she intended as the stimulus, thereby resulting in shorter RTs than her light stimulus alone might have produced. The magnitude of any such shift cannot be estimated. Obviously, visual RT depends on additional factors such as the length and distribution of foreperiods and the nature of the required response, as well as additional stimulus characteristics such as contrast with surroundings and stimulus size. Those
factors and others also likely vary among the data sets used by Woodley et al. (2013) as Dodonova and Dodonov (2013) discuss. Indeed we can see some indication of the power of other factors by looking again at some details of the data reported by Minucci and Connors (1964) and Cardello (1979). One of Minucci and Connors's stimuli was about double the luminance of one of Cardello's. Nonetheless, comparing the results across the studies at those two stimulus intensity levels, Minucci and Connors's subjects' mean RT was 235 ms whereas Cardello's subjects' mean RT was only 207 ms. Minucci and Connors's stimuli subtended a visual angle of 1° whereas Cardello's stimuli subtended a visual angle of 6°; Teichner and Krebs (1972) indicate that larger stimuli produce shorter RTs, so perhaps that contributed to the faster RTs reported by Cardello. Of the studies inventoried in Woodley et al. (2013) only Reed, Vernon, and Johnson (2004) specify the size of their stimuli. All their stimuli were smaller than 1°, and their mean reported RT was not notably long. As Dodonova and Dodonov (2013) noted, many details of experimental procedure influence the size of visual RT, and that makes it very difficult to draw firm conclusions about the source of differences in RT found by studies that differ in procedural details as well as year of data collection. The Victorians may well have been cleverer than us, but the visual RT data do not suffice to prove the point. References Cardello, A. V. (1979). Reaction time and visual brightness: Within-subject correlations. Perceptual and Motor Skills, 48, 107–115. Cattell, J. M. (1885). The influence of the intensity of the stimulus on the length of the reaction time. Brain, 8, 512–515. Dodonova, Y. A., & Dodonov, Y. S. (2013). Is there any evidence of historical slowing of reaction time? No, unless we compare apples and oranges. Intelligence, 41, 674–687. Dunlap, K., & Wells, G. (1910). Some experiments with reactions to visual and auditory stimuli. Psychological Review, 17, 319–335. Hick, W. E. (1952). On the rate of gain of information. Quarterly Journal of Experimental Psychology, 4, 11–26. Jensen, A.R. (2006). Clocking the mind: Mental chronometry and individual differences. Amsterdam: Elsevier. Johnson, R. C., McClearn, G. E., Yuen, S., Nagoshi, C. T., Ahern, F. M., & Cole, R. E. (1985). Galton's data a century later. American Psychologist, 40, 875–892. Luce, R. D. (1986). Response times: Their role in inferring elementary mental organization. Oxford UK: Oxford University Press. Mansfield, R. J. W. (1973). Latency functions in human vision. Vision Research, 13, 2219–2234. Minucci, P. K., & Connors, M. M. (1964). Reaction time under three viewing conditions: Binocular, dominant eye, and nondominant eye. Journal of Experimental Psychology, 67, 268–275. Neumann, O., & Niepel, M. (2004). Timing of “perception” and perception of “time”. In C. Kaernbach, E. Schröger, & H. Muller (Eds.), Psychophysics beyond sensation: Laws and invariants of human cognition. Mahwah NJ: Erlbaum. Reed, T. E., Vernon, P. A., & Johnson, A.M. (2004). Sex difference in brain nerve conduction velocity in normal humans. Neuropsychologica, 42, 1709–1714. Riggs, L. A. (1966). Light as a stimulus for vision. In C. H. Graham (Ed.), Vision and visual perception (pp. 1–38). New York: John Wiley & Sons. Scripture, E. W. (1895). Thinking, feeling, doing. Meadville PA: Flood and Vincent. Teichner, W. H., & Krebs, M. J. (1972). Laws of the simple visual reaction time. Psychological Review, 79, 344–358. Thompson, H. B. (1903). The mental traits of sex. An experimental investigation of the normal mind in men and women. Chicago IL: University of Chicago Press (Retrieved from http://library.manipaldubai.com/). Woodley, M.A., te Nijenhuis, J., & Murphy, R. (2013). Were the Victorians cleverer than us? The decline in general intelligence estimated from a meta-analysis of the slowing of simple reaction time. Intelligence, 41, 843–850. http://dx.doi.org/10.1016/j.intell.2013.04.006.
Contents lists available at ScienceDirect
Intelligence
Were the Victorians cleverer than us? Maybe, maybe not Scott Parker ⁎ Department of Psychology, American University, Washington DC 20016-8062, United States
a r t i c l e
i n f o
Article history: Received 6 March 2014 Received in revised form 18 June 2014 Accepted 18 August 2014 Available online xxxx
a b s t r a c t Woodley et al. (2013) noted an increasing trend in reported values of visual reaction times collected over 115 years and concluded that it indicated a decline of intelligence over that period. But because visual reaction times vary with a great many factors in addition to intelligence (notably stimulus luminance) that inference is underdetermined. © 2014 Elsevier Inc. All rights reserved.
Keywords: Dysgenic trend Simple visual reaction time Luminance
Contents
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Woodley, te Nijenhuis, and Murphy (2013) inventoried many studies of visual reaction time (RT) collected between the 1880s and 2004 and found a significant increase of RT over time. Their secular trend line gives trend-weighted mean RTs of about 193 ms in 1889 and about 270 ms in 2004—an increase of about 77 ms in a bit over a century. Because RT is known to be strongly related to intelligence (e.g., Jensen, 2006) the increase of RT over time might indicate that intelligence has declined over the last 120 years or so. However, visual RT is known to vary with many things other than intelligence. Dodonova and Dodonov (2013) discuss many of them. One important family of contributors is the characteristics of the visual stimulus to which the subjects react. Dodonova and Dodonov (2013) discuss many of those, based on a review of that literature by Teichner and Krebs ⁎ Tel.: +1 202 885 1719. E-mail address: [email protected].
http://dx.doi.org/10.1016/j.intell.2014.08.002 0160-2896/© 2014 Elsevier Inc. All rights reserved.
(1972). Prominent among those contributors is the luminance of the stimuli to which the subjects are to react. The idea that increasing stimulus intensity shortens reaction time is an old one. According to Neumann and Niepel (2004), results to that effect were found in the 1860s by Hirsch and the 1870s by Exner. Cattell (1885) reported data showing that trend. And Scripture (1895, p.48) wrote, “The intensity of the light has a very great influence. A very weak light might give 33 [hundredths of a second] while a strong one would give 20 [hundredths of a second] for the same person.” More recent work has confirmed that pattern. For example, Minucci and Connors (1964) showed a decrease of average binocular visual RT of about 60 ms as luminance of a 60-ms flash increased roughly a thousandfold (decrease for the dominant eye alone was about 80 ms and that for the nondominant eye was about 90 ms). Cardello (1979) showed a similar result for 1-second flashes—an average RT reduction of about 75 ms over a thousandfold increase in luminance. For approximately
2
S. Parker / Intelligence 47 (2014) 1–2
hundredfold changes in luminance, the RT reductions were about 35–40 ms in both studies. More extensive data is shown in both Mansfield (1973) and Teichner and Krebs (1972). Thousandfold changes in luminance are not so extreme as they might sound to people unfamiliar with them. A comfortable reading illumination is 1/1000 the luminance of a piece of white paper in sunlight but 1000 times the luminance of that white paper in moonlight. The human visual system is sensitive to an enormous range of luminances; a bright tungsten filament has 1013 times the luminance of a light at absolute threshold. (Riggs, 1966, p.26). Because of the dependence of visual RT on luminance, comparisons across studies of visual RT such as Woodley et al.'s (2013) should consider the luminances of the stimuli used in those studies. Sizeable differences in RT can arise from differences in the stimuli. With that in mind, I looked at the studies that Woodley et al. referred to and found, to my disappointment, that none of those studies specified the luminance of the stimuli. Dodonova and Dodonov (2013) say that we do not know enough about the studies used in Woodley et al. to estimate the variation in RT due to differences in stimulus luminance. Fig. 1 of Woodley et al. (2013) plots mean RT as a function of year for 16 data sets and exhibits a significant correlation between them. Inspection of that figure shows that there is an enormous range of mean RTs (a range of about 90 ms) reported by studies published between 1941 and 1945 and an even larger range (about 140 ms) reported by studies published between 1987 and 2004 (the newest studies used by Woodley et al.) Note that both of these ranges, observed in fairly narrow time periods, exceed the 77-ms shift in mean RT that Woodley et al. estimate to have occurred over the course of the 117 years from 1887 to 2004. Indeed, the observations that are crucial to the Woodley et al. (2013) finding are the earliest ones—those from Galton (as reported in Johnson et al., 1985) and Thompson (1903). Both of those data sets report very short reaction times and contribute greatly to the correlation between RT and year of report. Do those short reaction times betoken a high level of intelligence among the Victorians? In one of those cases, another factor may have contributed. Thompson (1903) generated her stimuli, flashes of purple light, using a Geissler tube—an ancestor of the fluorescent tube (Hick, 1952). But Dunlap and Wells (1910) chose to use a different light stimulus generator, explaining (p.320) that, “A Geissler tube could not be used, on account of the noise accompanying its flash.” Auditory RTs, like visual RTs, grow faster with increasing stimulus intensity (Luce, 1986). We would need to know both the auditory and visual intensities of the Geissler tube to know if Dunlap and Wells's concern was well-founded. But we cannot rule out the possibility that Thompson's subjects were reacting to a noise functionally more intense than the flash she intended as the stimulus, thereby resulting in shorter RTs than her light stimulus alone might have produced. The magnitude of any such shift cannot be estimated. Obviously, visual RT depends on additional factors such as the length and distribution of foreperiods and the nature of the required response, as well as additional stimulus characteristics such as contrast with surroundings and stimulus size. Those
factors and others also likely vary among the data sets used by Woodley et al. (2013) as Dodonova and Dodonov (2013) discuss. Indeed we can see some indication of the power of other factors by looking again at some details of the data reported by Minucci and Connors (1964) and Cardello (1979). One of Minucci and Connors's stimuli was about double the luminance of one of Cardello's. Nonetheless, comparing the results across the studies at those two stimulus intensity levels, Minucci and Connors's subjects' mean RT was 235 ms whereas Cardello's subjects' mean RT was only 207 ms. Minucci and Connors's stimuli subtended a visual angle of 1° whereas Cardello's stimuli subtended a visual angle of 6°; Teichner and Krebs (1972) indicate that larger stimuli produce shorter RTs, so perhaps that contributed to the faster RTs reported by Cardello. Of the studies inventoried in Woodley et al. (2013) only Reed, Vernon, and Johnson (2004) specify the size of their stimuli. All their stimuli were smaller than 1°, and their mean reported RT was not notably long. As Dodonova and Dodonov (2013) noted, many details of experimental procedure influence the size of visual RT, and that makes it very difficult to draw firm conclusions about the source of differences in RT found by studies that differ in procedural details as well as year of data collection. The Victorians may well have been cleverer than us, but the visual RT data do not suffice to prove the point. References Cardello, A. V. (1979). Reaction time and visual brightness: Within-subject correlations. Perceptual and Motor Skills, 48, 107–115. Cattell, J. M. (1885). The influence of the intensity of the stimulus on the length of the reaction time. Brain, 8, 512–515. Dodonova, Y. A., & Dodonov, Y. S. (2013). Is there any evidence of historical slowing of reaction time? No, unless we compare apples and oranges. Intelligence, 41, 674–687. Dunlap, K., & Wells, G. (1910). Some experiments with reactions to visual and auditory stimuli. Psychological Review, 17, 319–335. Hick, W. E. (1952). On the rate of gain of information. Quarterly Journal of Experimental Psychology, 4, 11–26. Jensen, A.R. (2006). Clocking the mind: Mental chronometry and individual differences. Amsterdam: Elsevier. Johnson, R. C., McClearn, G. E., Yuen, S., Nagoshi, C. T., Ahern, F. M., & Cole, R. E. (1985). Galton's data a century later. American Psychologist, 40, 875–892. Luce, R. D. (1986). Response times: Their role in inferring elementary mental organization. Oxford UK: Oxford University Press. Mansfield, R. J. W. (1973). Latency functions in human vision. Vision Research, 13, 2219–2234. Minucci, P. K., & Connors, M. M. (1964). Reaction time under three viewing conditions: Binocular, dominant eye, and nondominant eye. Journal of Experimental Psychology, 67, 268–275. Neumann, O., & Niepel, M. (2004). Timing of “perception” and perception of “time”. In C. Kaernbach, E. Schröger, & H. Muller (Eds.), Psychophysics beyond sensation: Laws and invariants of human cognition. Mahwah NJ: Erlbaum. Reed, T. E., Vernon, P. A., & Johnson, A.M. (2004). Sex difference in brain nerve conduction velocity in normal humans. Neuropsychologica, 42, 1709–1714. Riggs, L. A. (1966). Light as a stimulus for vision. In C. H. Graham (Ed.), Vision and visual perception (pp. 1–38). New York: John Wiley & Sons. Scripture, E. W. (1895). Thinking, feeling, doing. Meadville PA: Flood and Vincent. Teichner, W. H., & Krebs, M. J. (1972). Laws of the simple visual reaction time. Psychological Review, 79, 344–358. Thompson, H. B. (1903). The mental traits of sex. An experimental investigation of the normal mind in men and women. Chicago IL: University of Chicago Press (Retrieved from http://library.manipaldubai.com/). Woodley, M.A., te Nijenhuis, J., & Murphy, R. (2013). Were the Victorians cleverer than us? The decline in general intelligence estimated from a meta-analysis of the slowing of simple reaction time. Intelligence, 41, 843–850. http://dx.doi.org/10.1016/j.intell.2013.04.006.