Control & Response Selection

Transcription

1 Control & Response Selection Response Selection Response Execution 1 Types of control: Discrete Continuous Open-loop startle reaction touch typing hitting a baseball writing "motor programs" Closed-loop pushing a button "hunt & peck" typing "point & click" driving flying tracking 2 1

2 Issues in response selection: Decision complexity Response expectancy Compatibility Speed-accuracy tradeoff Feedback Task Environment Control design 3 Information display: decision complexity Information Theory (aka Communication Theory) Grew out of the study of problems of electrical communications (especially telegraphy) and statistical mechanics. message source encoder channel decoder message receiver The message source selects one of a possible set of messages, encodes it, and transmits the resulting signal through a channel. The message is decoded and then received by the receiver. 4 2

3 Information Theory: definitions Information: reduction of uncertainty (that the receiver has about the message transmitted by the source.) Bit: a single unit of information, equivalent to a choice between two alternatives (yes/no, on/off) Entropy (H): measure of information in bits (typically, bits per second, bits per word, bits per symbol) "a measure of our ignorance" H is based on the number of possible messages (or events or stimuli) N, the probabilities of those messages, and the context (i.e., the probabilities of all messages). 5 % Redundancy: % Redundancy=(1 - H H av max )* 100 SO WHAT? Why should we care? Because if we can quantify information, we can quantify human information processing!! In terms of performance, we can look at choice reaction time (how long it takes to make a choice or decision) as a function of the amount of information. Example: A tetris-like game is being designed in which the probability of appearance of each shape is directly proportional to the number of edges. If the pieces are shaped as follows, what is the average amount of information and the % redundancy in the system? 6 3

4 Quantifying information 7 For N equally likely alternatives, H = log log N = log If known probabilities: H = log 2 ( )= - log p N The "average entropy" of a system: 1 H av= pi [ log2 ( )] p i 2 2 i p i For example: If equally likely, H = If p i = [0.13, 0.2, 0.27, 0.4] H 1 = H av = Choice reaction time: The HICK-HYMAN LAW says that choice reaction time is a function of the amount of information in a stimulus: RT = a + b H where, H is the amount of information a is simple reaction time b is the slope of the function (the amount of added processing time for each bit of information.) Intuitively - the more choices we have, the longer it will take to choose from among them. 8 4

5 Choice reaction time example In the tetris-like game just described, the simple reaction time and the choice reaction time when all pieces are equally likely is measured. The results are as follows: simple reaction time, a = 300 msec. choice reaction time for equally likely events, Rt eq = 800 msec. Then the probability of appearance of the individual pieces is changed as described. What is the new expected choice reaction time? 9 Movement time: FITTS' LAW relates movement time to the distance and the size of the target. MT = a + b log 2 (2D/W) where, MT = movement time a & b = empirically derived constants D = distance of movement from start to target center W = width of the target Note: the term (2D/W) is sometimes referred to as the index of difficulty (ID), so that Fitts' Law becomes: MT = a + b log 2 (ID) 10 5

6 Movement time example W = _1 in_ D = _3.5 in_ a = 50 msec. MT = 200 msec. W = _0.5 in_ D = _7 in_ MT = 11 Movement time: Side Note: we might also use Schmidt's Law for movements executed so fast they cannot benefit from visual feedback W = a + b(d/mt) where W is now the effective target width or the "standard deviation of the end point dispersion..". 12 6

7 Continuous control Feedback control model for continuous control: Disturbance input Display Target Cursor Human operator Control Device System or Plant 13 Wickens et. al, pg. 274 Tracking: Pursuit vs Compensatory Pursuit - chasing the target Display tells you where you are in relation to the target Examples: driving, visual flight, tracing a path Compensatory - reducing the error Display tells you where you should be and the error Examples: aircraft instrument landing system, glide slope indicator; pong game

8 Input Frequency of movement of the target bandwidth of the input overshoot and undershoot errors depend on the range of magnitude changes time lag errors depend on the frequency of changes "Look-ahead" or prediction provide cues as to the direction and magnitude of the next change fewer and smaller errors smoother control motions 15 Control order (what type of controller is "best"?) 0-order (position) e.g., moving the mouse to a position on the screen Position 1st -order (velocity) e.g., joystick where increased control force increases the speed of response Position Time 2nd - order (acceleration) e.g, low speed ship steering, rocket maneuvering Position Time 16 Time 8

9 Problems of stability Closed-loop instability of the controlled system due to overcorrections, resulting in oscillations around the target. Due to: time lags - delay between control input and system response high gain - the system response to a given control input is too great for the operator to correctly control inappropriate operator response - too fast for system response, possibly due to combination of time lags and high input bandwidth Design guidelines to reduce instability reduce time lags through preview / predictor displays, better display design lower the gain change control strategy open loop operation 17 Control Input Devices Switch Voice Keyboard Mouse Knob Pointer Button Trackball/joystick 18 9

10 Buttons, switches, and knobs Recall design issues Physical feel Size Compatibility spatial, proximity pictorial realism, moving part frame of reference, conceptual (mental models) Affordances and constraints Movement time, reaction time 19 Keyboards and keypads Keyboards Purpose Layout QWERTY, DVORAK, alphabetic Keypads Purpose Layout telephone vs calculator Chordic keyboards 20 10

11 Mouse vs pointer For spatial tasks Direct vs indirect control Pointer (light pen, touch screen, etc.) direct control faster, but less accurate parallax errors size issues with touch screen best for more complex spatial control movements Mouse, touchpad, tablet indirect control more precise, but slower adjustable gain 21 Voice input BENEFITS Natural efficient dual task, time -sharing capability COSTS/ISSUES confusion, limited vocabulary size speed constraints acoustic quality (noise & stress) compatibility feedback and control technology limited 22 11

12 Technology issues in voice input Noise control Robust against drift (i.e., not affected by stress, natural changes in speaker voice.) Encoding, buffers, and editing Prompting (visual and auditory, etc.) and feedback Remote data entry Interruption allowance, continuous recognition, gender independence Customization (vocabulary, branching, applications, communication modes, etc.) Queuing of input data Help functions, ease of use, etc. (from: Pulat, B.M. (1997) Fundamentals of Industrial Ergonomics (2nd ed), Ch. 10. Prospect Heights, IL: Waveland Press.) 23 Control-display compatibility AKA Stimulus-Response Compatibility that is, what is the relationship between the stimulus (the content and format of the information) you receive and the response(s) available to you? affects learning, response time, errors, and preference We have already discussed several aspects of human information processing that apply sensory processing vision haptic/tactile senses etc. attention etc

13 Control-Display Design Principles Modality Compatibility degree to which the controls and displays utilize the same sensory modality. Within-modality stimuli-response relationships are generally faster, e.g., for verbal task: for spatial task: 25 Movement Compatibility relationships between movements of displays and controls where the direction of movement of a control follows from expectations, e.g. steering wheel turns car in direction of wheel movement. Movement of a control can: 1. follow - display movement as in radar tracking. 2. control - display movement as when moving a computer mouse to reposition a cursor. 3. produce - a specific system response such as turning a car steering wheel to turn a car in the same direction (it's the reverse on a boat)

14 Spatial Compatibility physical arrangement of controls and associated displays in space or physical similarity of displays and controls e.g., identify which controls should go with which display below 27 Rotary controls and rotary displays A. Fixed scales and moving pointers clockwise turn of pointer should result from clockwise turn of control and should represent and increase in the value. B. Moving scales and fixed pointers scale should rotate in the same direction as the control, scale numbers should increase from left to right, and a clockwise turn should increase the setting. Unfortunately, all three requirements can't be satisfied

15 Rotary controls and rotary displays (cont.) C. Rotary controls and linear displays in the same plane controls can be placed above, below, left or right of the display with fixedscale linear displays. 1. Warricks' principle (only applies when the control is located to the side of the display) 2. Scale-by-side-principle (applies to top and bottom control locations as well as to the side) 29 Rotary controls and rotary displays (cont.) D. Clock-wise for increase clock-wise movement of a rotary control will cause an increase in the value on the display irrespective of control display relations. E. Clock-wise - away and Counter-clock-wise - near clock-wise rotation suggests movement away from a person and counterclock-wise rotation suggests movement towards the person

16 Movements of displays and controls in different planes relationships tend to be orthogonal. Generally moving the control up and moving up on the display is superior to moving the control up and moving down on the display. There's less difference between moving the control forward to move the display up and moving the control forward to move the display down. Rotary and stick-type controls and linear displays several options, mostly following those recommendations for in the same plane 31 16