193
FACILITATING THE DISAPPEARANCE OF PERCEPTUAL ERROR TO THE POGGENDORFF ILLUSION TERRY W. MALLENBY Simon Fraser University The effect of verbal discussion more
facilitating
task. Results
are
on processing perceptual information proved to be than were social facilitation or sensorimotor tracing of an illusory summarized in terms of perceptual developmental models.
The Poggendorff illusion, as noted by Bayer (1972), is produced by interrupting two portions of a straight oblique line by two vertical parallel lines, as shown in Fig. la. Judd (1902) initially demonstrated that an illusion disappears with practice, as a result of perceptual development (i.e., maturation), rather than as a result of a judgmental process (such as practice). A later investigation of the Poggendorff, however, has only confirmed this fact with adult subjects (Pressey and Sweeney, 1969), and not with children (Pressey and Sweeney, 1970). Recently, Bayer (1972) has suggested that the developmental theory of Werner (1961; Wapner and Wemer, 1957; Wemer and Kaplan, 1967) offers a suitable perceptual explanation and model for this contradiction. Specifically, in terms of information processing, children are at a lower developmental level than adults; their perceptions are, therefore, more global, resulting in rigid perceptual activity. Since children are developmentally too immature to recognise or appreciate that the Poggendorff phenomenon is actually an illusion, practice effects do not reduce the number of
errors on the illusion, as does occur with adults. Adults, on the other hand, advanced developmentally. The efficacy of their information processing, subsequently, is assumed to be greater, producing more flexible perceptual activity and, therefore, greater improvement with practice. Although both Judd (1902) and Bayer (1972) have cited perceptual models in explanation of the disappearance of the illusory effects of two different illusions (i.e., Mueller-Lyer and Poggendorff, respectively), no one has yet made the logical extension, and examined the forms of behavioural mediation that might facilitate the perceptual process. Langer (1962) and Miller (1959), former students of Werner’s, for example, have suggested that as hierarchically integrated levels of perceptual development are attained, verbal mediation plays an increasingly active role in the abstract analysis of information, permitting the flexible responses typical of adults. In this regard, the present study was designed to examine the effect of discussion between subjects about the Poggendorff illusion, with specific reference to the reduction of errors to the illusion for this group.
are more
Sub jects Sixty boys
from
two
grade six classes
at a
normal
public
school served
as
subjects.
194
Fig.
1.
(a) Poggendorff illusion; (b)
Po stimulus
card; (c) Pr stimulus card.
They were divided into three groups, ranging in age from 11 yrs. 1 mth. to 14 yrs. 5 mths., the mean being 12 yrs. 1 mth. None of the subjects wore glasses.
Apparatus Two 8 in. by 11 in. stimulus cards were employed. One illustrated the Poggendorff illusion, shown in Fig. la. The dimensions of the illusion were identical to that used by Pressey and Sweeney (1969). It consisted of two 7 in. parallel vertical lines,
1.125 in. apart. A 1.5 in. diagonal line joined the vertical line on the left at a distance of 1.5 in. from the top of that line. The angle formed by the diagonal and vertical lines was 20°. The second stimulus card was a Practice card for the Poggendorff illusion, which appears in Fig. 1 c. It had the same dimensions as the Poggendorff illusion card, except that the oblique line in the Poggendorff card was now perpendicular to the left vertical line and joined that line at a distance of 3.5 in. from the top. Procedure The subjects were initially divided into three groups of 20 boys each. Subjects from the first group were examined individually and were not permitted to discuss their responses; this group will be referred to hereafter as Individually-Non discussion.
195 groups were examined in pairs, however, those from group discuss their answers, whereas, those from group three permitted These groups will be referred to as In pairs-Non discussion and In pairs-
Subjects
from the other
two
two were not were.
to
Discussion, respectively. The experimental room
consisted of a private office (approximately 12 ft. by 12 ft.) in the school. There was one desk and a suitable number of chairs for the experimenter and subjects. The subject(s) sat to the experimenter’s right, while illumination was supplied by normal fluorescent lighting, plus a large window directly behind the
participants. The stimuli (the Poggendorff illusion cards and Practice cards) were not presented in a confining apparatus, as was used by Pressey, Bayer and Kelm (1969), but were rather presented in an unrestricted situation. Specifically, the stimulus cards, which were initially hidden from view, were presented directly to the subject’s visual field face up on the table. For each of the six presentations of identical Poggendorff illusion cards (i.e., practice effect), the subjects were required to mark a fine, but well-defined, dot on the right vertical line at the point where the oblique line would joint if it were extended. Subjects were required to respond after viewing each stimulus card for 10 sec. All instructions were given verbally so that queries could be answered immediately. If, for example, any of the children did not understand the task, the experimenter simplified the instructions by saying, &dquo; See this little line (while pointing to the perpendicular line on the Practice card)? Where would it cross this larger line on the right (while pointing to the right vertical line), if it were extended? &dquo; Before the Poggendorff illusion cards were exhibited, the experimenter demonstrated the task with a Practice stimulus card. The subjects were also required to respond to one Practice card to make sure they understood the task. Specific instructions for each group were as follows: Individually-Non discussion, subjeats were instructed that they were not to touch the stimulus cards until the experimenter had told them to make their response; In pairs-Non discussion, subjects were instructed not to discuss their responses, but were permitted to trace the illusion with their fingers, in order to facilitate the analysis of the illusion. Alternate subjects responded after the required time interval had elapsed; In pairs-Discussion, subjects were also examined in pairs. They were instructed to describe their reasons to the other subject, discuss their perceptions, and finally come to an agreement as to where the response dot was to be marked (in order to establish a reference point during these discussions, the subjects were permitted to touch the right vertical line only). After the required time had elapsed, alternate subjects were asked to record their agreed upon response. Since agreement between the subjects was the major concern for this third group before a response was given, the 10 sec. viewing interval was not strictly adhered to. It was noted, however, that near the end of the stimulus presentations (i.e., successive trials or practice effect), consensus between the subjects had occurred before the compulsory interval had expired.
196
Fig.
2. Mean size of the illusion for each group
over
successive trials.
RESULTS Measurements were accurate to within 0.125 in. The mean error size to the illusion for each group over successive trials (i.e., practice) appears in Fig. 2. It is clear that the Individually-Non discussion and the In pairs-Non discussion groups, which were not permitted to discuss their responses, perceived a greater degree of distortion to the illusion than did the In pairs-Discussion group, which had been permitted to discuss their responses. (F The effect of practice 8.22; d.f. 2,47; p
FACILITATING THE DISAPPEARANCE OF PERCEPTUAL ERROR TO THE POGGENDORFF ILLUSION TERRY W. MALLENBY Simon Fraser University The effect of verbal discussion more
facilitating
task. Results
are
on processing perceptual information proved to be than were social facilitation or sensorimotor tracing of an illusory summarized in terms of perceptual developmental models.
The Poggendorff illusion, as noted by Bayer (1972), is produced by interrupting two portions of a straight oblique line by two vertical parallel lines, as shown in Fig. la. Judd (1902) initially demonstrated that an illusion disappears with practice, as a result of perceptual development (i.e., maturation), rather than as a result of a judgmental process (such as practice). A later investigation of the Poggendorff, however, has only confirmed this fact with adult subjects (Pressey and Sweeney, 1969), and not with children (Pressey and Sweeney, 1970). Recently, Bayer (1972) has suggested that the developmental theory of Werner (1961; Wapner and Wemer, 1957; Wemer and Kaplan, 1967) offers a suitable perceptual explanation and model for this contradiction. Specifically, in terms of information processing, children are at a lower developmental level than adults; their perceptions are, therefore, more global, resulting in rigid perceptual activity. Since children are developmentally too immature to recognise or appreciate that the Poggendorff phenomenon is actually an illusion, practice effects do not reduce the number of
errors on the illusion, as does occur with adults. Adults, on the other hand, advanced developmentally. The efficacy of their information processing, subsequently, is assumed to be greater, producing more flexible perceptual activity and, therefore, greater improvement with practice. Although both Judd (1902) and Bayer (1972) have cited perceptual models in explanation of the disappearance of the illusory effects of two different illusions (i.e., Mueller-Lyer and Poggendorff, respectively), no one has yet made the logical extension, and examined the forms of behavioural mediation that might facilitate the perceptual process. Langer (1962) and Miller (1959), former students of Werner’s, for example, have suggested that as hierarchically integrated levels of perceptual development are attained, verbal mediation plays an increasingly active role in the abstract analysis of information, permitting the flexible responses typical of adults. In this regard, the present study was designed to examine the effect of discussion between subjects about the Poggendorff illusion, with specific reference to the reduction of errors to the illusion for this group.
are more
Sub jects Sixty boys
from
two
grade six classes
at a
normal
public
school served
as
subjects.
194
Fig.
1.
(a) Poggendorff illusion; (b)
Po stimulus
card; (c) Pr stimulus card.
They were divided into three groups, ranging in age from 11 yrs. 1 mth. to 14 yrs. 5 mths., the mean being 12 yrs. 1 mth. None of the subjects wore glasses.
Apparatus Two 8 in. by 11 in. stimulus cards were employed. One illustrated the Poggendorff illusion, shown in Fig. la. The dimensions of the illusion were identical to that used by Pressey and Sweeney (1969). It consisted of two 7 in. parallel vertical lines,
1.125 in. apart. A 1.5 in. diagonal line joined the vertical line on the left at a distance of 1.5 in. from the top of that line. The angle formed by the diagonal and vertical lines was 20°. The second stimulus card was a Practice card for the Poggendorff illusion, which appears in Fig. 1 c. It had the same dimensions as the Poggendorff illusion card, except that the oblique line in the Poggendorff card was now perpendicular to the left vertical line and joined that line at a distance of 3.5 in. from the top. Procedure The subjects were initially divided into three groups of 20 boys each. Subjects from the first group were examined individually and were not permitted to discuss their responses; this group will be referred to hereafter as Individually-Non discussion.
195 groups were examined in pairs, however, those from group discuss their answers, whereas, those from group three permitted These groups will be referred to as In pairs-Non discussion and In pairs-
Subjects
from the other
two
two were not were.
to
Discussion, respectively. The experimental room
consisted of a private office (approximately 12 ft. by 12 ft.) in the school. There was one desk and a suitable number of chairs for the experimenter and subjects. The subject(s) sat to the experimenter’s right, while illumination was supplied by normal fluorescent lighting, plus a large window directly behind the
participants. The stimuli (the Poggendorff illusion cards and Practice cards) were not presented in a confining apparatus, as was used by Pressey, Bayer and Kelm (1969), but were rather presented in an unrestricted situation. Specifically, the stimulus cards, which were initially hidden from view, were presented directly to the subject’s visual field face up on the table. For each of the six presentations of identical Poggendorff illusion cards (i.e., practice effect), the subjects were required to mark a fine, but well-defined, dot on the right vertical line at the point where the oblique line would joint if it were extended. Subjects were required to respond after viewing each stimulus card for 10 sec. All instructions were given verbally so that queries could be answered immediately. If, for example, any of the children did not understand the task, the experimenter simplified the instructions by saying, &dquo; See this little line (while pointing to the perpendicular line on the Practice card)? Where would it cross this larger line on the right (while pointing to the right vertical line), if it were extended? &dquo; Before the Poggendorff illusion cards were exhibited, the experimenter demonstrated the task with a Practice stimulus card. The subjects were also required to respond to one Practice card to make sure they understood the task. Specific instructions for each group were as follows: Individually-Non discussion, subjeats were instructed that they were not to touch the stimulus cards until the experimenter had told them to make their response; In pairs-Non discussion, subjects were instructed not to discuss their responses, but were permitted to trace the illusion with their fingers, in order to facilitate the analysis of the illusion. Alternate subjects responded after the required time interval had elapsed; In pairs-Discussion, subjects were also examined in pairs. They were instructed to describe their reasons to the other subject, discuss their perceptions, and finally come to an agreement as to where the response dot was to be marked (in order to establish a reference point during these discussions, the subjects were permitted to touch the right vertical line only). After the required time had elapsed, alternate subjects were asked to record their agreed upon response. Since agreement between the subjects was the major concern for this third group before a response was given, the 10 sec. viewing interval was not strictly adhered to. It was noted, however, that near the end of the stimulus presentations (i.e., successive trials or practice effect), consensus between the subjects had occurred before the compulsory interval had expired.
196
Fig.
2. Mean size of the illusion for each group
over
successive trials.
RESULTS Measurements were accurate to within 0.125 in. The mean error size to the illusion for each group over successive trials (i.e., practice) appears in Fig. 2. It is clear that the Individually-Non discussion and the In pairs-Non discussion groups, which were not permitted to discuss their responses, perceived a greater degree of distortion to the illusion than did the In pairs-Discussion group, which had been permitted to discuss their responses. (F The effect of practice 8.22; d.f. 2,47; p
