Viously. In this case, the sample consisted of two stimuli (e.g., AB) and the choice array contained three stimuli, one of which matched one of the samples (e.g., A, C, E on some trials, and B, D, F on others). Overselective attending to A would result in Isovaleryl-Val-Val-Sta-Ala-Sta-OH supplier approximately 100 correct responding when the array contained A, but chance levels (33 ) when the array contained B. With both types of trials equally represented, the mean overall purchase Leupeptin (hemisulfate) accuracy score would be approximately 67 (see Dickson, Deutsch, et al. 2006 for further details of the accuracy score analysis). The eye-tracking data for these participants showed that the great majority of errors occurred on trials when the participant fixated on only one of the two sample stimuli. These failures to observe one of the samples occurred on 32 to 60 of the trials across participants. Other errors on a smaller number of trials followed relatively brief observing durations (< 100 ms). Data analysis showed that the overselectivity was closely linked to inadequate observing behavior. On the subset of trials on which only one sample stimulus was observed and that stimulus was also the correct comparison, mean accuracy for the six participants was 98 ; on the trials with only one sample observed and that stimulus was not included as a comparison, mean accuracy was 33 (chance level). The overall intermediate accuracy scores resulted from averaging these two types of trials. When observing occurred, attending was reliable. Behavior and Eye Tracking Research: Observing Duration and Behavioral Flexibility A second eye tracking study, Dube et al. (2006), further illuminates the issues of observing and attending. This study includes data on the relation between two different aspects of observing that are relevant to AAC instruction: eye movements while observing the stimuli within an array, and other behavior that ends the opportunity to observe. The latter is often a manual response to the device displaying the stimuli. For example, when selecting a symbol from an AAC array, the individual first scans the array to locate the symbol. Upon manual selection of the target symbol, the scanning period is terminated. As the number of stimuli in the display changes, optimal performance requires flexibility in both the trajectory of the scanning behavior and the timing of the selection response. In Dube et al. (2006), four adults without disabilities were tested with the same matching-tosample procedure described above and shown in Figure 1: At the beginning of each trial, two sample stimuli were presented and remained displayed until the participant touched theNIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptAugment Altern Commun. Author manuscript; available in PMC 2015 June 01.Dube and WilkinsonPagescreen. Then the samples disappeared and the comparison stimuli were presented. Different stimuli appeared on every trial. All four had high accuracy scores (96 to 100 ).NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptNext, the number of samples was suddenly increased from two to four per trial. Accuracy scores remained high for two participants (92 ) but fell to intermediate levels for two others (63 and 67 ). Thus, overselectivity was temporarily (see below) provoked in participants without disabilities by an abrupt increase in task complexity. Eye-tracking analyses of the first session with four-sample trials showed that all of the participants made simil.Viously. In this case, the sample consisted of two stimuli (e.g., AB) and the choice array contained three stimuli, one of which matched one of the samples (e.g., A, C, E on some trials, and B, D, F on others). Overselective attending to A would result in approximately 100 correct responding when the array contained A, but chance levels (33 ) when the array contained B. With both types of trials equally represented, the mean overall accuracy score would be approximately 67 (see Dickson, Deutsch, et al. 2006 for further details of the accuracy score analysis). The eye-tracking data for these participants showed that the great majority of errors occurred on trials when the participant fixated on only one of the two sample stimuli. These failures to observe one of the samples occurred on 32 to 60 of the trials across participants. Other errors on a smaller number of trials followed relatively brief observing durations (< 100 ms). Data analysis showed that the overselectivity was closely linked to inadequate observing behavior. On the subset of trials on which only one sample stimulus was observed and that stimulus was also the correct comparison, mean accuracy for the six participants was 98 ; on the trials with only one sample observed and that stimulus was not included as a comparison, mean accuracy was 33 (chance level). The overall intermediate accuracy scores resulted from averaging these two types of trials. When observing occurred, attending was reliable. Behavior and Eye Tracking Research: Observing Duration and Behavioral Flexibility A second eye tracking study, Dube et al. (2006), further illuminates the issues of observing and attending. This study includes data on the relation between two different aspects of observing that are relevant to AAC instruction: eye movements while observing the stimuli within an array, and other behavior that ends the opportunity to observe. The latter is often a manual response to the device displaying the stimuli. For example, when selecting a symbol from an AAC array, the individual first scans the array to locate the symbol. Upon manual selection of the target symbol, the scanning period is terminated. As the number of stimuli in the display changes, optimal performance requires flexibility in both the trajectory of the scanning behavior and the timing of the selection response. In Dube et al. (2006), four adults without disabilities were tested with the same matching-tosample procedure described above and shown in Figure 1: At the beginning of each trial, two sample stimuli were presented and remained displayed until the participant touched theNIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptAugment Altern Commun. Author manuscript; available in PMC 2015 June 01.Dube and WilkinsonPagescreen. Then the samples disappeared and the comparison stimuli were presented. Different stimuli appeared on every trial. All four had high accuracy scores (96 to 100 ).NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptNext, the number of samples was suddenly increased from two to four per trial. Accuracy scores remained high for two participants (92 ) but fell to intermediate levels for two others (63 and 67 ). Thus, overselectivity was temporarily (see below) provoked in participants without disabilities by an abrupt increase in task complexity. Eye-tracking analyses of the first session with four-sample trials showed that all of the participants made simil.
