Age changes in the Poggendorff illusion as measured by a method of production

the control group on this trial. This isolation effect was significant, t( 200) = 3.02. p < .0 I. While treatments were again the same for experimental and control groups on the post-isolation trials. 10 through 12, these trials were analyzed to determine if there were any residual cffects from the previous isolation. Though from examination of Fig. I, one might consider the experimental group to have sligh t1y better STM on Trial II than the control group, ANOVA on the three post-isolation trials indicated that the groups and trials effects as well as their interaction were not significant. p>.1 0 in all th ree cases. Therefore. any apparent differences on post-isolation trials were attributed to chance factors. When a more lenient criterion of STM, number of correct letters irrespective of their positions, was used, similar results were obtained throughout. DISCUSSION The results of the present experiment demonstrate that perceptually isolating an item increases its STM. Turvey & Egan (1969). in a similar experiment. using slide area as the means of perceptual isolation, a 10-sec recall period, and no post-isolation trials. also found improved STM for perceptually isolated items, lending furt her support for the present finding. Unfortunately. Turvey and Egan 's measure of STM is questionable. A score of 2 was given to each letter of the CCC in its correct position and a score of I to each correct letter in an incorrect position. This assurnes equivalence between one letter in its correct position (score = 2) and two letters in incorrect positions (score = 2), an assumption that would be difficult to justify. Furthermore, while this measure allows scores ranging from 0 to 6, a score of 5 is impossible, raising some question about the scale. I ncreasing the saliency of an item through perceptual isolation facilitates STM of that item. It is possible that better STM of an item involving a sudden change in conceptual dass might also be attributable to increased attention to that item, rather than to a reduction of semantic interference effects from previous items. If this were the case, the findings of improved STM for an item differing in conceptual dass from previously presen ted items (e.g., Loess, 1968; Wickens & Ekler, 1968; Wickens & Simpson, 1968) could easily be reconciled with findings of little or no semantic interference effects in STM (e.g., BaddeJey, 1964; Baddeley, 1966; Gumenik. 1969). A further finding of the present experiment was that there was no significant differences of isolating an itcm Psychon. Sei., 1970, Vol. 19 (2) on the STM of post-isolation items. This may be analogous to thc failure of several, but not all. investigators to find effects of stimulus isolation on non-isolated items (e.g., Gumenik & Levit!, 1968). The prescnt STM task differed greatly from the usual serial or paired-associate learning situation in which isolation effects are found in that the present task did not involve repetition of the same items over severaJ trials. Also, the present STM task involved the discrete recall of individual items rather than the learning of an entire list of items simultaneously. However, the similarity of isolation effects in the present STM task and in serial and paired-associate learning suggest that the same mechanism may be involved. One possible mechanism that might be operating in these disparate tasks couId be akin to the "attention-getting value" of the isoIated item suggested by Green (1958), which might enhance both STM of the item and the learning of the item in the repeated trials of a scrial or paired-associate task. REFERENCES BADDELEY. A. D. Semantic and acoustic similarity in short-term memory. Nature, 1964. 204. 1116-1117. BADDELEY, A. D. Short-term memory for word sequenees as a function of acoustic. semantie and formal similarity. Quarterly Journal of Experimental Psyehology, 1966, 18, 362-365. GREEN, R. T. The attention-getting value of ,tructural change. British Journal of P'ychology. 1958.49. 311-314. Gl"~ENIK. W. E. Effects of articulatory activity and auditory, visual and semantic similarity on Ihe short-term memory of visually presented paired associates. Journal 01' Experimental Psychology. 1969.82,70-74. GUMENIK. W. E., & LEVlTT, J. The von Restorff effeet as a funetion of difference of the bola ted item. American Journal of P'ychology. 1968,81,247-252. LOESS. 11. Short-term memory and item similarity. Journal of Verbal Learning & Verbal Behavior, 1968,7,87-92. TURVEY. M. T., & EGAN, J. Contextual change and release from proactive interference in short-term verbal memory. Journal of Experimental Psyehology, 1969,81,396-397. UNDERWOOD, B. J., & SCHULZ, R. W. Meaningfulness and verbal learning: Chicago: Lippincott, 1960. WICKENS, D. c., & EKLER, M. R. Semantic as opposed to aeoustic encoding in STM. Psychonomie Scienee, 1968, 12, 63. WICKENS, D. 0_, & SIMPSON, H. K. Semantic vs. phonetic eneoding in short term memory. Paper presented at the meeting of the Midwestern Psyehological Association, SI. Louis. 1968. NOTE I. Thc au thors wish to thank Patricia Mundelius for her assistanee in computing the data. Age changes in the Poggendorff illusion as measured by a method of production A_ W. PRESSEyl and O. SWEENEY, University of Manituba, Winnipeg 19, Canada Children at three age levels were tested on the Poggendorff illusion with a methud of production. The illusion decreased with age; this supports previous investigations in which the method of adiustment was used. A sex difference of marginal significance was found, bllt the illusion did not change as a function of sllccessive trials. 1t was concluded that the method of production is a valid means of measuring the Poggendorff illusion. If two portions of a single oblique line are interrupted by two separa te parallel lines, the two obliques do not appear collinear. Su.:h a .:onfiguration is known as the Poggendorff illusion and is illustrated in Fig. IA. Traditionally, the method of adjustment has been employed to measure the illusion, but recently a method of production has been employed (Pressey & Sweeney, 1969). Herc. one of the obliques is removcd. as shown in Fig. I B, and S is required to place a do! on the right vertical line so that the oblique on the left appears to point to it. There are several advantages to the method of production. First, complex, bulky and expensive equipment is not required. Second, the time necessary to test a S is greatly reduced, and finally, the production method might easily lend itself to group testing. The major question A B Fig_ I. The c1assical version (A) and a variation-(B) of the Poggendorff illusion. 99 that remains, however, is whether or not the same functional relationships are obtained as with other psychophysieal methods. The purpose of this study was to d e t e r mine the relationship between chronological age and the Poggendorff illusion. Leibowitz & Gwozdecki (1967) and Vurpillot (1957), both employing the me (...truncated)