PHYSIOLOGICAL OPTICS

Transcription

1 DEPARTMENT OF VISION SCIENCES SESSION: 2004/2005 DIET: 2ND PHYSIOLOGICAL OPTICS VISP325 LEVEL: 3: MODULE LEADER: PROF G HERON B.Sc./B.Sc. (HONS) OPTOMETRY AUGUST 2005 DURATION: 3 HOURS CANDIDATES SHOULD ATTEMPT FIVE QUESTIONS IN TOTAL AND AT LEAST ONE QUESTION FROM EACH SECTION PLEASE READ THE QUESTIONS CAREFULLY MATERIALS TO Lined Examination Script Books BE SUPPLIED/ALLOWED: Unlined Examination Script Books Other Materials, e.g. Graph paper, statistical tables (please specify) Page 1 of 5

2 SECTION A 1. a) Show the pattern of inheritance of the sex linked recessive trait of congenital red/green colour vision deficiency. (10) b) Show why the prevalence in females is much lower than it is in males. (2) c) Give reasons why this prevalence is even lower than predicted from the prevalence values of male colour vision deficiency. (8) 2. Describe and discuss Hurvich & Jameson s model of colour vision. (20) In writing your answer you might find it helpful to consider the following: How is this model related to Helmhotz s trichromatic and Hering s colouropponent theories? What is the physiological evidence supporting the Hurvich and Jameson model? Page 2 of 5

3 SECTION B 3. Using the idea of a temporal window or summation time, explain why a highly sensitive light detecting system necessarily has low temporal resolution, and why a high temporal resolution system necessarily has low sensitivity. Illustrate your answer with a drawing and a numerical example. (20) 4. Describe an experiment which measures contrast sensitivity in the laboratory. The aim of the experiment is to use contrast adaptation to explore how the visual system analyses contrast and spatial frequency. Illustrate your answer with diagrams where possible. a) Describe in detail the stimulus and method you would use to measure contrast sensitivity for a range of spatial frequencies. (4) b) How can the effects of adaptation to spatial frequency be assessed? (4) c) Give some typical results of spatial frequency adaptation experiments. (6) d) What have results from these experiments told us about the organisation of the visual system for spatial vision? (6) Page 3 of 5

4 SECTION C 5. a) Describe (including the specific application for elucidating the structure in question), with illustrations as appropriate, procedures which can be used to determine the following features of area V1 (primary, or striate visual cortex). YOU SHOULD ONLY ANSWER FOR 3 OF THE FOLLOWING 5 FEATURES i) How the visual field is mapped onto the cortex; ii) iii) iv) The layers. (i.e. determine that there are separate layers); The ocular dominance columns; Orientation columns; v) Blobs and interblobs. Don t discuss more than one technique per property. You may use the same technique for more than one property but must describe the distinct details of its application and data collected for each different property. For those techniques where multiple data must be taken to determine structure, explain how the data are combined to determine the property you re investigating. (15) b) Briefly describe the functional organisation of area V2 and relate it to relevant aspects of the organisation of V1. (5) 6. This question concerns motion processing: a) In which area of the brain would one be certain that all the cells would respond to the direction of motion? (2) b) Describe (in detail) three experiments which would support the view that cells in this area are involved in the perception of motion. (9) c) Draw a neuronal circuit which ends with a cell responsive to motion. Include a sketch of a sample stimulus as it would appear to the retina, clearly labelling receptive fields for the cells in your circuit. Explicitly indicate the nature of the connections between cells. (9) Page 4 of 5

5 SECTION D 7. a) What is the basic tenet of Gestalt theory of visual perception? (2) b) Who were its three main proponents? (3) c) Show how Julesz s Texton theory is related to Gestalt psychology (15) 8. What are the main features that distinguish Marr s computational approach to vision from earlier approaches? (20) Your answer should address: what is the purpose of visual perception according to Marr? Also, what are (i) primal sketch, (ii) 2 1 / 2 D-sketch, and (iii) 3D model representation? END OF PAPER Page 5 of 5