Sensorimotor representation and knowledge-based reasoning for spatial exploration and localisation.

We investigate a hybrid system for autonomous exploration and navigation, and implement it in a virtual mobile agent, which operates in virtual spatial environments. The system is based on several distinguishing properties. The representation is not map-like, but based on sensorimotor features, i.e. on combinations of sensory features and motor actions. The system has a hybrid architecture, which integrates a bottom-up processing of sensorimotor features with a top-down, knowledge-based reasoning strategy. This strategy selects the optimal motor action in each step according to the principle of maximum information gain. Two sensorimotor levels with different behavioural granularity are implemented, a macro-level, which controls the movements of the agent in space, and a micro-level, which controls its eye movements. At each level, the same type of hybrid architecture and the same principle of information gain are used for sensorimotor control. The localisation performance of the system is tested with large sets of virtual rooms containing different mixtures of unique and non-unique objects. The results demonstrate that the system efficiently performs those exploratory motor actions that yield a maximum amount of information about the current environment. Localisation is typically achieved within a few steps. Furthermore, the computational complexity of the underlying computations is limited, and the system is robust with respect to minor variations in the spatial environments.

Catching audiovisual mice: predicting the arrival time of auditory-visual motion signals.

We investigated the extent to which auditory and visual motion signals are combined when observers are asked to predict the location of a virtually moving target. In Condition 1, the unimodal and bimodal signals were noisy, but the target object was continuously visible and audible; in Condition 2, the virtually moving object was hidden (invisible and inaudible) for a short period prior to its arrival at the target location. Our main finding was that the facilitation due to simultaneous visual and auditory input is very different for the two conditions. When the target is continuously visible and audible (Condition 1), the bimodal performance is twice as good as the unimodal performances, thus suggesting a very effective integration mechanism. On the other hand, if the object is hidden for a short period (Condition 2) and the task therefore requires the extrapolation of motion speed over a temporal and spatial period, the facilitation due to both sensory inputs is almost absent, and the bimodal performance is limited by the visual performance.

Quality of life after treatment for advanced laryngeal and hypopharyngeal cancer.

OBJECTIVES: To compare health-related quality of life measures after treatment for advanced (stages III and IV) laryngeal and hypopharyngeal cancers. STUDY DESIGN: Retrospective chart review and patient response to Health Status Questionnaire-12 (HSQ-12). METHODS: Our study included 54 patients identified from the Tumor Registry of the University of Louisville Brown Cancer Center who were diagnosed and treated between 1995 and 2000. Demographics, tumor data, and treatment information were obtained from the Tumor Registry database. Questionnaires were mailed to all patients and included telephone follow-up. Comparative data and responses were analyzed for the 24 patients who responded to the survey. RESULTS: Fifteen patients were treated with chemotherapy and radiation therapy (CRT). Six patients underwent surgery with postoperative radiation therapy (SRT). The remaining three patients were treated with radiation therapy but were not used in this analysis. The average follow-up was 35 months after treatment. The CRT and SRT groups were statistically similar regarding age, sex, duration of follow-up, tumor grade, and tumor stage. Laryngeal primary tumors were more common in the SRT group than in the CRT group (P =.005). Eight domains were assessed by the HSQ-12: physical functioning, role-physical, bodily pain, health perception, energy/fatigue, social functioning, role-mental, and mental health. No statistical differences were found between the CRT and SRT groups, except for role limitations attributable to physical health (P =.007). CONCLUSIONS: These results indicate that only one of eight domains differs significantly between treatment groups when using the HSQ-12. Two-year survival end-point analysis of global health assessment may represent a simplified and meaningful way to compare treatment modalities in patients with advanced-stage head and neck cancer.

Minimally invasive radioguided parathyroidectomy.

BACKGROUND: Minimally invasive radioguided parathyroidectomy (MIRP) combines technetium sestamibi scan, intraoperative gamma probe, methylene blue dye, and measurement of circulating parathyroid hormone (PTH) levels. STUDY DESIGN: All patients presented with biochemically proved primary hyperparathyroidism. A technetium sestamibi scan was performed preoperatively. Technetium sestamibi and methylene blue dye (7.5 mg/kg) were administered IV on the day of operation. Operative dissection was directed by the gamma probe. Blood samples for PTH assay were obtained before and after excision of an abnormal gland. When an appropriate decrease in the PTH assay was obtained, the exploration was concluded. Persistent PTH elevation instigated further neck exploration. RESULTS: Thirty-six consecutive patients were explored for untreated primary hyperparathyroidism and three for recurrent hyperparathyroidism. Hypercalcemia was corrected in all 39 patients. A single adenoma was found in 32 of 36 patients with untreated primary hyperparathyroidism, and a single abnormal gland was identified in all of those with recurrent hyperparathyroidism. Persistently elevated PTH prompted further exploration in two patients, identifying a second abnormal gland in one and hyperplasia in the other. Minor local complications occurred in 8% (3 of 39) of the patients. Forty-four percent (16 of 36) of the patients were discharged on the day of operation and 83% (30 of 36) within 23 hours after the initial neck exploration for primary hyperparathyroidism. Comparison of charges for MIRP with charges for "standard" neck exploration revealed lower costs with MIRP because of decreased duration of the operation, anesthesia, and hospital stay, and elimination of intraoperative histologic analysis. CONCLUSIONS: MIRP is a safe and effective procedure, resulting in the correction of hypercalcemia in all patients. The combination of intraoperative gamma probe and methylene blue dye allows rapid identification of the abnormal gland with minimal dissection through a small incision. PTH assay after excision provides biochemical confirmation that the abnormal gland has been removed. Most patients undergoing MIRP can be treated on an outpatient basis. Low postoperative complications, a small incision, and rapid return to normal activities resulted in very high patient acceptance of the procedure.

Object and scene analysis by saccadic eye-movements: an investigation with higher-order statistics.

Based on an information theoretical approach, we investigate feature selection processes in saccadic object and scene analysis. Saccadic eye movements of human observers are recorded for a variety of natural and artificial test images. These experimental data are used for a statistical evaluation of the fixated image regions. Analysis of second-order statistics indicates that regions with higher spatial variance have a higher probability to be fixated, but no significant differences beyond these variance effects could be found at the level of power spectra. By contrast, an investigation with higher-order statistics, as reflected in the bispectral density, yielded clear structural differences between the image regions selected by saccadic eye movements as opposed to regions selected by a random process. These results indicate that nonredundant, intrinsically two-dimensional image features like curved lines and edges, occlusions, isolated spots, etc. play an important role in the saccadic selection process which must be integrated with top-down knowledge to fully predict object and scene analysis by human observers.

A model of visual spatio-temporal memory: the icon revisited.

With a minimal set of assumptions resulting from considerations about the perception of temporal structure, we argue for the existence of a spatio-temporal memory established by the mapping of time into simultaneous physical properties. The important point of this model is the distinction between external, physical time and the internal representation of time. An immediate consequence of such a structure is the emergence of properties usually associated with the concept of iconic memory or informational persistence. Some of these properties may hence be regarded as epiphenomena produced by the testing of a spatio-temporal system with tachistoscopic spatial stimuli. The model can explain properties of the immediate memory span, the lack of effect of exposure duration on tachistoscopic report, the partial-report superiority, the decay of iconic memory, and effects of a backward mask. It does not only avoid the incompatibility problems of the frozen-image concept in dynamic vision, but also provides an adequate basis for the processing of time-varying scenes.

Multistable states in intrahemispheric learning of a sensorimotor task.

We have obtained evidence from an intrahemispheric learning task using a choice-reaction-time paradigm that the acquisition of a sensorimotor skill can be discontinuous. Subjects had to react as fast as possible to either a visual or an auditory stimulus. In several successive sessions, reaction times improved markedly, however in a discontinuous way. Different levels of performance were characterized by discrete functional states, each state being associated with a particular temporal window. After sufficient learning, reactions were confined to the earlier of two such windows.