Biomedical subjects

Frank H Baker

Publications and source records attributed to Frank H Baker.

5 recordsLinked to original sources

PubMed2005

Visual disability variables. I: the importance and difficulty of activity goals for a sample of low-vision patients.

OBJECTIVE: To test the validity and reliability of latent trait measures estimated from ratings by low-vision patients of the importance and difficulty of selected activity goals. DESIGN: Validation of a telephone-administered functional assessment instrument using Rasch analysis of self-assessment ratings. SETTING: Telephone interviews of respondents in their homes. Participants Consecutive series of 600 outpatients with low vision. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Ratings of the importance and difficulty of achieving 41 activity goals. Person and item traits were measured with the Andrich rating scale model. Measurement validity and reliability were tested statistically by comparing response patterns and distributions with measurement model expectations. RESULTS: Patients could distinguish only 3 categories of importance and 4 categories of difficulty. The distributions of person and item measure fit statistics were consistent with 2 unidimensional constructs: value of independence estimated from importance ratings and visual ability estimated from difficulty ratings. However, 8 of 41 activity goals were poor estimators of value of independence and 7 of 41 activity goals were poor estimators of visual ability. Person measure distributions could be divided into 3 statistically distinct strata for estimates from both importance ratings and difficulty ratings. Item measure distributions could be divided into 21 strata for estimates from importance ratings and 7 strata for estimates from difficulty ratings. CONCLUSIONS: The 2 variables that define visual disability-value of independence and visual ability-are valid constructs that can be estimated accurately and reliably from patient ratings of the importance and difficulty of activity goals.

Activities of Daily Living↗

PubMed2005

Visual disability variables. II: The difficulty of tasks for a sample of low-vision patients.

OBJECTIVES: To test the validity and reliability of measures of visual ability and to evaluate the relation between measurements made at the task level and measurements made at the goal level of a hierarchical model for visual disability. DESIGN: Validation of a telephone-administered functional assessment instrument using Rasch analysis on self-assessment ratings. SETTING: Telephone interviews of respondents in their homes. PARTICIPANTS: Consecutive series of 600 outpatients with low vision. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Ordinal ratings of the difficulty in performing a subset of 337 tasks. Measures of the visual ability of each patient and the required visual ability to perform each task were made using the Andrich rating scale model. Measurement validity and reliability were tested statistically by comparing response patterns and distributions to measurement model expectations. RESULTS: Results were consistent with a single visual ability construct. Patients' visual ability estimated from task difficulty ratings agreed with estimates from goal difficulty ratings ( r =.74); the difficulty of individual goals was equal to the weighted average of the difficulties of subsidiary tasks ( r =.79). However, conclusions from the Rasch analysis were not confirmed by principal components analysis of item residuals, which indicated that visual ability had a 2-dimensional structure, with 1 factor related to mobility and the other related to reading. Factor analysis on person measures estimated from subsets of functionally grouped items confirmed the 2-dimensional structure of visual ability. CONCLUSIONS: Our study results confirm the hierarchical structure of the Activity Breakdown Structure model and show how the individualized Activity Inventory can produce measures of limitations in functional vision.

Activities of Daily Living↗

PubMed2003

Oculomotor strategies for the direction of gaze tested with a real-world activity.

Laboratory-based models of oculomotor strategy that differ in the amount and type of top-down information were evaluated against a baseline case of random scanning for predicting the gaze patterns of subjects performing a real-world activity--walking to a target. Images of four subjects' eyes and field of view were simultaneously recorded as they performed the mobility task. Offline analyses generated movies of the eye on scene and a categorization scheme was used to classify the locations of the fixations. Frames from each subject's eye-on-scene movie served as input to the models, and the location of each model's predicted fixations was classified using the same categorization scheme. The results showed that models with no top-down information (visual salience model) or with only coarse feature information performed no better than a random scanner; the models' ordered fixation locations (gaze pattern) matched less than a quarter of the subjects' gaze patterns. A model that used only geographic information outperformed the random scanner and matched approximately a third of the gaze patterns. The best performance was obtained from an oculomotor strategy that used both coarse feature and geographic information, matching nearly half the gaze patterns (48%). Thus, a model that uses top-down information about a target's coarse features and general vicinity does a fairly good job predicting fixation behavior, but it does not fully specify the gaze pattern of a subject walking to a target. Additional information is required, perhaps in the form of finer feature information or knowledge of a task's procedure.

Adult↗

PubMed2002

Fixation behavior while walking: persons with central visual field loss.

The aim of this study was to determine the effect of central visual field loss (CFL) on fixation patterns of a person walking towards a target. Subjects were four visually normal persons and 10 persons with CFL. Eye position on scene was recorded and classified into 20 scene categories. The distributions of fixations among scene categories were compared across the two subject groups. For all but two CFL subjects, who fixated primarily at the floor, the distributions of fixations for the CFL subjects ranged from being moderately to strongly correlated with that of the visually normal mean. An analysis of the similarity in the sequence of fixations (or gaze pattern) of the CFL subjects to the visually normal subjects showed a range of 7-66%. Excluding the one CFL subject who had a functioning fovea, sequence similarity was strongly correlated with the logarithm of the minimum angle of resolution (logMAR). The better a person's logMAR, the more closely his or her gaze pattern matched that of the visually normal subjects. Finally, the CFL data were tested against two current models of oculomotor strategy, visual salience and guided search. Similar to what was found with visually normal subjects, CFL subjects appear to use the expected features and general location of the target to guide their fixations, the guided-search strategy.

Adolescent↗

PubMed1994

The sensation of angina can be evoked by stimulation of the human thalamus.

We have performed single-neuron recording and microstimulation in the region of the thalamic principal sensory nucleus (ventrocaudal nucleus, Vc) prior to implantation of a deep brain-stimulating electrode in a patient with pain secondary to arachnoiditis and with a past history of unstable angina. Cells located in the 16 mm lateral plane had cutaneous receptive fields on the chest wall. At and posterior to the location of these cells stimulation coincided precisely with the sensation of angina (stimulation-associated angina). The description of stimulation-associated angina was measured using a questionnaire and was identical to the patient's usual angina except that it began and terminated suddenly. Stimulation-associated angina was coincident with a tingling sensation in the leg. Clinical, hemodynamic, electrophysiologic and biochemical measures of cardiac function showed no evidence of myocardial strain or injury related to stimulation-associated angina. Since cells in the region of the principle sensory nucleus of thalamus respond to cardiac injury in animals, the present results suggest that this region mediates the sensation of angina.

Aged↗