title: A contrast-sensitive, redundancy reduction mechanism acting on MT neurons can explain global motion direction biases without the need for Bayesian priors

authors: Perrone, John A.

subjects: Bayesian observer model

abstract: Introduction: The perceived global direction of moving objects can be influenced by the contrast of the object (Weiss, Simoncelli & Adelson, Nature Neuroscience, 2002). There is currently no detailed, neural-based explanation for how this could occur. Weiss et al., proposed an ideal Bayesian observer model that included a physiologically unspecified ‘low speed’ prior. We have recently developed a new velocity code for extracting image velocity from small groups of MT neurons (Perrone & Krauzlis, VSS 2011). The code includes a stage of local spatial inhibition between MT neurons designed to reduce the amount of redundant signals passed onto the global motion integration stage (MST). The inhibition is made dependent upon the contrast of the stimulus by exploiting the fact that some MT neurons change their speed tuning (V shifts to ∼ .5V) at low contrast (Krekelberg et al., J. Neurosci., 2006). An inhibitory signal based on the difference in output from two such MT units tuned to V and 2V will be high at high contrast, but will switch off at low contrast when the input speed is V.
Methods: We tested our velocity code using high- and low-contrast rhombus stimuli that have been shown to produce contrast dependent biases in global motion estimates (Weiss, et al., 2002).
Results: The model produced contrast dependent estimates of global motion direction that match the perceptual results. Low contrast rhomboids tended to produce estimates orthogonal to the major axis of the rhombus whereas high contrast rhomboids produced estimates closer to the veridical direction. Our simulations indicate that at low contrast the spatial inhibitory mechanisms between MT neurons may be switching off causing an increase in the density of responses signalling motion orthogonal to the edges.
Conclusion: Our model provides a biologically plausible mechanism by which the Weiss et al., Bayesian prior could be implemented.

text: A contrast-sensitive, redundancy reduction mechanism acting on MT neurons can explain global motion direction biases without the need for Bayesian priors Introduction: The perceived global direction of moving objects can be influenced by the contrast of the object (Weiss, Simoncelli & Adelson, Nature Neuroscience, 2002). There is currently no detailed, neural-based explanation for how this could occur. Weiss et al., proposed an ideal Bayesian observer model that included a physiologically unspecified ‘low speed’ prior. We have recently developed a new velocity code for extracting image velocity from small groups of MT neurons (Perrone & Krauzlis, VSS 2011). The code includes a stage of local spatial inhibition between MT neurons designed to reduce the amount of redundant signals passed onto the global motion integration stage (MST). The inhibition is made dependent upon the contrast of the stimulus by exploiting the fact that some MT neurons change their speed tuning (V shifts to ∼ .5V) at low contrast (Krekelberg et al., J. Neurosci., 2006). An inhibitory signal based on the difference in output from two such MT units tuned to V and 2V will be high at high contrast, but will switch off at low contrast when the input speed is V.
Methods: We tested our velocity code using high- and low-contrast rhombus stimuli that have been shown to produce contrast dependent biases in global motion estimates (Weiss, et al., 2002).
Results: The model produced contrast dependent estimates of global motion direction that match the perceptual results. Low contrast rhomboids tended to produce estimates orthogonal to the major axis of the rhombus whereas high contrast rhomboids produced estimates closer to the veridical direction. Our simulations indicate that at low contrast the spatial inhibitory mechanisms between MT neurons may be switching off causing an increase in the density of responses signalling motion orthogonal to the edges.
Conclusion: Our model provides a biologically plausible mechanism by which the Weiss et al., Bayesian prior could be implemented.

year: 2012

title: Object/picture recognition in hens

authors: Railton, R.

subjects: conditional discrimination

abstract: Two experiments examined whether hens, Gallus gallus domesticus, would respond to photographs in the same way they do to the real objects depicted in the photographs. Experiment 1 assessed whether hens transferred a discrimination of differently coloured three-dimensional objects to two-dimensional photographs of those objects, and vice versa. All hens learned to discriminate between the stimuli and showed transfer to the alternative stimuli when the colour cues were present. In Experiment 2 transfer with stimuli that differed in shape only was examined. It was found that only three of the six hens learned to discriminate the stimuli to any degree, and that these three hens did not transfer this discrimination to the alternative stimuli. It was also found that previously learning an object discrimination did not aid the hens in learning to discriminate between photographs of the objects. These data suggest that the hens did not respond to the objects depicted in pictures in the same way they did to the real objects. The authors argue it cannot be assumed that all animals respond to two-dimensional pictures of stimuli in the same way as they do to the real three-dimensional stimuli and this should be established before researchers use two-dimensional stimuli as representatives of real world stimuli.

text: Object/picture recognition in hens Two experiments examined whether hens, Gallus gallus domesticus, would respond to photographs in the same way they do to the real objects depicted in the photographs. Experiment 1 assessed whether hens transferred a discrimination of differently coloured three-dimensional objects to two-dimensional photographs of those objects, and vice versa. All hens learned to discriminate between the stimuli and showed transfer to the alternative stimuli when the colour cues were present. In Experiment 2 transfer with stimuli that differed in shape only was examined. It was found that only three of the six hens learned to discriminate the stimuli to any degree, and that these three hens did not transfer this discrimination to the alternative stimuli. It was also found that previously learning an object discrimination did not aid the hens in learning to discriminate between photographs of the objects. These data suggest that the hens did not respond to the objects depicted in pictures in the same way they did to the real objects. The authors argue it cannot be assumed that all animals respond to two-dimensional pictures of stimuli in the same way as they do to the real three-dimensional stimuli and this should be established before researchers use two-dimensional stimuli as representatives of real world stimuli.

year: 2014

title: Exploring patient experiences and power dynamics in an acute general surgical ward: A mixed methods study exploring patient and staff
perceptions of the inpatient experience at Waikato Hospital

authors: Drake, Emma Rose

subjects: Nursing

abstract: Background: Alongside health outcomes, patient experiences are considered crucial in identifying the quality of a health care setting. General surgery comprise the largest range of pathologies and accounts for the highest number of patient discharges of any surgical specialty. As a way to address the power imbalance between healthcare staff and patients, patient-centred models of care are increasingly being adopted and implemented within hospitals including surgery. This study aims to investigate the current experiences of acutely admitted patients in a general surgical ward at Waikato Hospital, including opportunities for and challenges to improvement initiatives. Furthermore, the study examines relevant staff members perspectives of the inpatient experience and seeks to determine the efficacy of a proposed intervention focusing on empowering patients and their families.
Methods: The study was a mixed method design involving two phases. Phase I obtained qualitative data from semi-structured interviews with six patients and twelve staff members. Themes which emerged from the qualitative data in phase I were used to inform the development of phase II, as well as to inform a proposed patient self- assessment intervention. Phase II obtained quantitative data through Likert scale response surveys provided to acute patients on, or near to, their day of discharge from the surgical ward over a two month period.
Results: A total of six patients and 12 healthcare staff (senior registered nurses, n=3; surgical registered nurse managers, n=2; surgical fellows, n=2; surgical registrar, n=1; dietitian, n=1; social worker, n=1; occupational therapist, n=1; and physiotherapist n=1) were involved in phase I. A total of 53 surveys were returned from patients in Phase II (63.1% response rate). Qualitative data from phase I was analysed using a general inductive approach. This revealed three themes including power and control concerns for patients, the hierarchy of the health care team and the surrounding stressors of the organisation and environment. Analysis of the quantitative data collected descriptive statistics and calculated chi-squares. Of note were the statistically significant differences particularly between patients of Māori ethnicity comparatively to non-Māori, and according to gender and reason in hospital. There were no statistically significant differences for patients according to age group.
Conclusion: This study identified both the experiences of patients and staff in an acute general surgical context. The study found that the proposed patient self- assessment intervention was not immediately recommended. This was due to the current recommendations from patients who identified their strong preference was for face-to-face communication with staff. It was also due to staff members identification of a perceived inability to consistently provide person-centred care which corresponded with the patient self-assessment data. Acute general surgical care needs of patients were perceived by staff as taking precedent and current workplace stressors, including staffing and skill mix deficits and perceived lack of staff wellbeing supports, were strong inhibitors for staff to provide their preferred capacity of patient-centred care.

text: Exploring patient experiences and power dynamics in an acute general surgical ward: A mixed methods study exploring patient and staff
perceptions of the inpatient experience at Waikato Hospital Background: Alongside health outcomes, patient experiences are considered crucial in identifying the quality of a health care setting. General surgery comprise the largest range of pathologies and accounts for the highest number of patient discharges of any surgical specialty. As a way to address the power imbalance between healthcare staff and patients, patient-centred models of care are increasingly being adopted and implemented within hospitals including surgery. This study aims to investigate the current experiences of acutely admitted patients in a general surgical ward at Waikato Hospital, including opportunities for and challenges to improvement initiatives. Furthermore, the study examines relevant staff members perspectives of the inpatient experience and seeks to determine the efficacy of a proposed intervention focusing on empowering patients and their families.
Methods: The study was a mixed method design involving two phases. Phase I obtained qualitative data from semi-structured interviews with six patients and twelve staff members. Themes which emerged from the qualitative data in phase I were used to inform the development of phase II, as well as to inform a proposed patient self- assessment intervention. Phase II obtained quantitative data through Likert scale response surveys provided to acute patients on, or near to, their day of discharge from the surgical ward over a two month period.
Results: A total of six patients and 12 healthcare staff (senior registered nurses, n=3; surgical registered nurse managers, n=2; surgical fellows, n=2; surgical registrar, n=1; dietitian, n=1; social worker, n=1; occupational therapist, n=1; and physiotherapist n=1) were involved in phase I. A total of 53 surveys were returned from patients in Phase II (63.1% response rate). Qualitative data from phase I was analysed using a general inductive approach. This revealed three themes including power and control concerns for patients, the hierarchy of the health care team and the surrounding stressors of the organisation and environment. Analysis of the quantitative data collected descriptive statistics and calculated chi-squares. Of note were the statistically significant differences particularly between patients of Māori ethnicity comparatively to non-Māori, and according to gender and reason in hospital. There were no statistically significant differences for patients according to age group.
Conclusion: This study identified both the experiences of patients and staff in an acute general surgical context. The study found that the proposed patient self- assessment intervention was not immediately recommended. This was due to the current recommendations from patients who identified their strong preference was for face-to-face communication with staff. It was also due to staff members identification of a perceived inability to consistently provide person-centred care which corresponded with the patient self-assessment data. Acute general surgical care needs of patients were perceived by staff as taking precedent and current workplace stressors, including staffing and skill mix deficits and perceived lack of staff wellbeing supports, were strong inhibitors for staff to provide their preferred capacity of patient-centred care.

year: 2022