fig. 1 Horizontal & Line. The first line bisection task with a horizontal line and a moveable perpendicular.
Patston, Corballis, Hogg, and Tippett (2006) found that in a line bisection task, musicians made a rightward error in placing a perpendicular bisector while the general, non-musician, population made a leftward error.
The rightward error was also found in participants who were stroke patients (Wang, Sonoda, Hanamura, Okazaki, and Saitoh, 2005), dyslexic children (Sireteanu, Goertz, Bachert, Wandert, 2005), right posterior cortex damaged participants (Luh, 1995), and severe schizophrenics (Harriett, 2006). Leftward line-bisection errors were found in normal subjects (Chidester, 1934; Luh, 1995; Hausmann, 2003).
In addition to the rightward bias, Patston showed musicians were more accurate at bisecting the lines. This study attributed the greater accuracy of line bisection to the proposed greater spatial attention of musicians. Our study wishes to confirm the rightward musician bias as well as investigate its proposed causes. We believe that by adding a second horizontal line with the perpendicular in between, we would increase the rightward bias of musicians. This belief is based on the idea that horizontal lines with vertical lines on them represent the language of music: the music staff and bar lines. We hypothesize that by adding another horizontal connected on the top of the perpendicular that it will increase this rightward error of musicians because it is a closer approximation of a staff and bar line.
Forty musicians of at least two years of proficient music reading ability and musicianship, and forty non-musicians with less than two years of music reading ability participated in the experiment.
The line-bisection was performed using Eye Lines Mac 3.2 (Beagley, 2003) software. The first line bisection task had one horizontal line displayed on the computer screen with a moveable perpendicular line for the participant to adjust to the perceived middle of the horizontal line (Horizontal & Line see fig. 1). The second line bisection task also consisted of a horizontal line, but it had a small perpendicular dash that was moveable along the horizontal in order for the participant to place the dash in the perceived center (Horizontal & Dash see fig. 2). The third figure consisted of two horizontal lines with the moveable perpendicular line between the two horizontal (Two Horizontals see fig. 3). Each figure was presented on the screen eight random times with the perpendicular starting place along the line randomly presented and determined by the Eye Lines software for a total of twenty-four.
Participants were directed to use the vertical line/dash divide the horizontal line into two equal parts. After each of the twenty-four figures they were directed to hit return
fig. 1 Horizontal & Line.
The first line bisection task with a horizontal line and a moveable perpendicular.
fig. 2 Horizontal & Dash.
The second line bisection task with a horizontal and a moveable dash.
fig. 3 Two Horizontals.
The third line bisection task with two horizontal lines and one moveable perpendicular.
Musicians showed a rightward deviation on all figures while the non-musicians showed a leftward deviation from the center on all figures. See fig 4. Differences among the figures did exist. Horizontal & Line (fig 1.) for musicians had an average rightward deviance of 13.28 mm; Horizontal & Dash (fig 2.) had a rightward deviance of 22.02 mm while Two Horizontals (fig 3.) had a rightward deviance of 28.58 mm. Non-musicians showed differences among the figures as well. Horizontal & Line (fig 1.) for non-musicians showed a leftward deviance of 11.81 mm. Horizontal & Dash (fig 2.) showed a leftward deviance of 21.4 mm while Two Horizontals (fig 3.) had a leftward deviance of 7.46 mm.
Musicians showed a greater deviation to the right than non-musicians showed to the left. Between the two groups their accuracy was determined by the average of all of the scores. The musicians had an average of 21.4 mm to the right of center while non-musicians were more accurate and had an average to the left of center of 13.6 mm.
The mean percentage of deviation from the true center of the horizontal line was determined by division of the averages between groups and figures by the horizontal line length (100 mm). See figure 4. Musicians’ percentage of deviation for Horizontal & Line (fig 1.) is 13.3%; Horizontal & Dash (fig.2) is 22%; and Two Horizontals (fig. 3) is 28.6%. Non-Musicians’ percentage of deviation to the left for Horizontal & Line (fig 1.) is 11.8%; Horizontal & Dash (fig.2) is 21.4 %; Two Horizontals (fig. 3) is 7%.
These results confirm the prior left bias (Patston, 2006; Chidester, 1934; Luh, 1995; Hausmann, 2003). They also confirm the right bias in musicians’ found by Patston (2006).
Some findings were novel compared to Patstons. Patston found that musicians were more accurate in line bisection tasks then non-musicians. In this study they were found to have a greater average error, 21.4 mm, than non-musicians, 13.6 mm error.
This data also showed that perhaps there are other factors influencing musicians in line bisection tasks. Non-musicians when presented with the Two Horizontal stimuli (fig. 3) actually had greater accuracy bisecting the line, but musicians had less accuracy in the same task. Their rightward error increased to 28.58 mm from the previous scores of 22.02 and 13.28 mm for musicians. This rightward error may be present because of the similarity between the figure three stimuli and that of a staff and bar line in music. A bar line in music is placed at the end of the measure and would separate number of beats per measure. Musicians would read this music and anything after a bar line would be considered separate and unimportant to the moment. Since these figures represent a language to the musician it might present a reason for the rightward error. The non-musicians did not show an increase in their leftward error when presented with figure three and their scores were closest to the true center of the line when presented with figure three, 7.46 to the left. All participants bisected the horizontal line of Two Horizontals further to the right than in the other variations. Perhaps the addition of the second horizontal makes the general population view the center of the figure further right than they would without the second horizontal.
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