title: Changeover delay and concurrent schedules

authors: Scown, Jan Marie

abstract: Domestic hens served as subjects in a series of three experiments investigating the effects of changeover delay (COD) on concurrent variable-interval schedule performance. The first experiment involved manipulations of the relative reinforcement rates on the two schedules presented on two separate keys while holding the COD constant over a series of COD durations from no COD to 15-sec. Sensitivity to reinforcement as measured by a in the generalised matching law was, for both response and time measures, less than unity and least at no COD. Generally it increased with the introduction of any COD but did not change systematically with COD length. Responding during the COD was found to be insensitive to changes in reinforcement rate ratios. The second experiment manipulated the stimuli presented on the main key during the COD (CO-key procedure). Adding distinctive key-colours during the COD increased sensitivity to reinforcement while the addition of blackout decreased time (but not response) sensitivity. Both effects carried over into following (non-stimulus) conditions but this did not survive a change in the schedules. The third experiment held the schedule values constant (two-key procedure) while the COD values were varied from no COD to 12-sec (thrice). Measures of behaviour changed with COD value although generally the a values were similar to those of the first experiment. Overall the changes were recoverable although individual point estimates of a were shown not to be reliable. The findings from the three experiments support the use of the generalised matching law to describe performance on concurrent schedules of
reinforcement. They also question the common use of changeover delays in concurrent schedules in that they appear to do more than simply separate the schedules in time.

text: Changeover delay and concurrent schedules Domestic hens served as subjects in a series of three experiments investigating the effects of changeover delay (COD) on concurrent variable-interval schedule performance. The first experiment involved manipulations of the relative reinforcement rates on the two schedules presented on two separate keys while holding the COD constant over a series of COD durations from no COD to 15-sec. Sensitivity to reinforcement as measured by a in the generalised matching law was, for both response and time measures, less than unity and least at no COD. Generally it increased with the introduction of any COD but did not change systematically with COD length. Responding during the COD was found to be insensitive to changes in reinforcement rate ratios. The second experiment manipulated the stimuli presented on the main key during the COD (CO-key procedure). Adding distinctive key-colours during the COD increased sensitivity to reinforcement while the addition of blackout decreased time (but not response) sensitivity. Both effects carried over into following (non-stimulus) conditions but this did not survive a change in the schedules. The third experiment held the schedule values constant (two-key procedure) while the COD values were varied from no COD to 12-sec (thrice). Measures of behaviour changed with COD value although generally the a values were similar to those of the first experiment. Overall the changes were recoverable although individual point estimates of a were shown not to be reliable. The findings from the three experiments support the use of the generalised matching law to describe performance on concurrent schedules of
reinforcement. They also question the common use of changeover delays in concurrent schedules in that they appear to do more than simply separate the schedules in time.

year: 1983

title: Video-based detection of shorelines at complex mesomacro tidal beaches

authors: Almar, Rafael

subjects: intertidal beach morphology

abstract: Remote video imagery is widely used to acquire measurements of intertidal topography by means of shoreline detection, but, up to now, problems of accuracy were still encountered in the challenging case of energetic waves in nonuniform, mesomacro tidal environments. Unique, simultaneous, video-based and global positioning system (GPS)based measurements of shoreline were undertaken at Truc Vert (France), a beach with such characteristics. An innovative video method, referred to herein as the Minimum Shoreline Variability (MSV) method, was developed to cope with highly variable spatiotemporal shoreline properties. The comparison of video-based and GPS-derived shoreline data sets showed that using images averaged over short periods (30 s), rather than the traditionally used 10-min averaged images, significantly improved the accuracy of shoreline determination. A local video-derived, swash-based shoreline correction was also developed to correct for the MSV error, which was found to be linearly correlated to local swash length. By combining shorter time-averaged images and video derived local swash correction factors, the horizontal root mean square error associated with MSV shorelines was reduced to 1.2 m, which is equivalent to errors reported at more uniform, microtidal, and less-energetic beaches.

text: Video-based detection of shorelines at complex mesomacro tidal beaches Remote video imagery is widely used to acquire measurements of intertidal topography by means of shoreline detection, but, up to now, problems of accuracy were still encountered in the challenging case of energetic waves in nonuniform, mesomacro tidal environments. Unique, simultaneous, video-based and global positioning system (GPS)based measurements of shoreline were undertaken at Truc Vert (France), a beach with such characteristics. An innovative video method, referred to herein as the Minimum Shoreline Variability (MSV) method, was developed to cope with highly variable spatiotemporal shoreline properties. The comparison of video-based and GPS-derived shoreline data sets showed that using images averaged over short periods (30 s), rather than the traditionally used 10-min averaged images, significantly improved the accuracy of shoreline determination. A local video-derived, swash-based shoreline correction was also developed to correct for the MSV error, which was found to be linearly correlated to local swash length. By combining shorter time-averaged images and video derived local swash correction factors, the horizontal root mean square error associated with MSV shorelines was reduced to 1.2 m, which is equivalent to errors reported at more uniform, microtidal, and less-energetic beaches.

year: 2012

title: Listening and Learning from Rangatahi Māori: the Voices of Māori Youth

authors: Berryman, Mere

subjects: student self-determination

abstract: This paper presents three stories-over-time of the secondary schooling experiences of New Zealand’s rangatahi Māori–or Māori youth. The stories span fifteen years of New Zealand schooling and are told from three perspectives: the experiences of the students as told in their own words; the voices of youth within the prevailing political contexts of government policy; and, the reframing and repositioning of researchers listening to the experiences of rangatahi Māori who believe they have succeeded as Māori. In reality, the stories are interwoven, however, in an effort to make sense of the various methodological dilemmas, risks, and entanglements across the three points of learning, we have endeavored to disentangle these different threads from the whole and follow these independent of each other. We then weave these threads together again, as we sense-make across this complexity to identify implications for other educators, policy makers and researchers.

text: Listening and Learning from Rangatahi Māori: the Voices of Māori Youth This paper presents three stories-over-time of the secondary schooling experiences of New Zealand’s rangatahi Māori–or Māori youth. The stories span fifteen years of New Zealand schooling and are told from three perspectives: the experiences of the students as told in their own words; the voices of youth within the prevailing political contexts of government policy; and, the reframing and repositioning of researchers listening to the experiences of rangatahi Māori who believe they have succeeded as Māori. In reality, the stories are interwoven, however, in an effort to make sense of the various methodological dilemmas, risks, and entanglements across the three points of learning, we have endeavored to disentangle these different threads from the whole and follow these independent of each other. We then weave these threads together again, as we sense-make across this complexity to identify implications for other educators, policy makers and researchers.

year: 2017