Behavioral Aspects of Text Editors

David W. Embley, George NagyUniversity of Nebraska, Lincoln

Assumptions for readers

• Familiar with basic vocabulary of computer science

• Sufficient exposure to various text and program editors

• Innocent of any formal training in psychology

QED, CMS, TECO, Wylbur, WIDJET and UNIX

Interactive Text Editors

• Frequently, Primary means of interaction with computer– Manuscript creation– Programming– File System Maintenance– Email

• Important to make their use easy• Editors

– General Purpose Interactive editors• QED, CMS, TECO, Wylbur, WIDJET and UNIX

– Language dependent editors• BASIC, APL, LISP

Editor Design and Evaluation

• Everyone has an opinion, but no consensus• Some established means:

– Introspection– Field Studies/Observations– Formal Analysis– Controlled Experiments– Psychological Models

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IntrospectionOur own intuition and experience, is what we depend on when we assume that we know as much about the topic as the next person and are too lazy to look further

Psychological ModelsCharacterize human performance

Goal: To predict human behavior in a restricted environment while performing a set of tasks

Example ( of an editing task)

Applicable areas of Psychology

• Cognitive Psychology– Study of higher mental processes– LLUMPRT

• Well studied area but limited application to study of text editors

Overview

• Section 1 : Temporal Models

• Section 2: Impact of Editor structure and command languages– How do different editors differ ?

• Section 3: Stimulus and response studies of input devices : Mouse wins

Performance Time Considerations

Objective

• To minimize the time incurred by a user performing a number of editing tasks over a period of time

• Depends on numerous factors• Expertise of the user• Learning methods and procedures• User alertness and motivation• Out of Paper• …

• Some are within our control and can be improved

Predictive Models

The Keystroke Model [CARD]

Total time = sum of time required to perform individual unit tasks

To acquire a mental representation of the task Perform and execute it

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Example

• Replacing one word of arbitrary length with a five letter word

Model Verification

• 12 subjects, 4 different editing tasks, 3 different editors

• Tasks:– Simple word substitution– Moving a sentence

Results

• Observed times and predicted times match mostly

• Exploring More or less detailed models [CARD]

The Embley Model

• A simpler model for line-oriented editors

• Objective– Comparing program editor performance as a

function of time required by a user to perform editing tasks

The Model

Acquisition time and mental time combined

m = number of command response pairs

Tc = delay per command = mental prep. Time + computer response time

n = number of keystrokes

Tk = time per keystroke

GOMS Model

• Attempts to explain How an expert user accomplishes routine editing tasks, not just time constituents

Can adjust to desired level of detail

• Example

Substitute

OR

Specify substitute command – specify argument number 1 - specify argument number 2 – enter command

Which one is more accurate ??

Experimental Studies

• Several variations were explored• 10 different GOMS models

– 16 second operator duration, 8, 4, 2, 0.5 ( “type an ‘s’, home hands on keyboard)

• 5 participated, only 1 studied

DATA

Derivation Data Cross-validationData

Prediction rules for operator sequences

Estimates for operator duration

For calculation of unit task time using derivation data results

Predicting the task accomplishment method

• Objective: To determine whether a set of simple selection rules could account for the methods user select.

• The Experiment– 3 subjects– Teletypewriter and CRT

Findings

• Each subject appeared to have a dominant method – the first rule

• S2 applied different dominant method for different devices – speed difference

• Selection of methods depends on feature of task – e.g. : – Locating a line : number of lines between current

line and target line

Users are able to quickly select near-optimal methods by having assimilated heuristic rules based on a few pertinent task features

Contribution of Errors

• Error ignored in previous experiments• Even for experts: 5-30% time in errors and

error corrections

For accurate Prediction, errors must also be considered

Roberts’s Experiments

• 4 experts 4 separate tasks• Human observer noted time consumed by

significant errors (> 30 seconds )

• Findings : Much of the subject-to-subject variation is due to error rates– For error free data, variation can be attributed to editors

than to the subjects

Applying the Keystroke model• Errors were ignored• Optimal Method prediction Predictions 25-30%

too low• Actual key sequence records only 87%

accounted for.• Remaining time Unknown mental activities

Advantage of Keystroke Model

• Assumes that user is so practiced that:– Method selection time would be nil– Choices optimal– Entry Flawless

• Provides an upper bound for the editing time• Comparison between predicted time and

observed time relatively large difference indicates that editor is difficult to use optimally

Effects of Computer Response time

Effects of Computer Response time

• System Delay and Unpredictability Affects user Productivity and Satisfaction

• Editing : Any perceptible delay may prove irritating

• R.B. Miller Immediate response is not a universal requirement in interactive computing

• Lists various class of user actions and allowable delays “best guesses”

Miller’s experiment

• Effects of varying CRT display rates and output delays on user performance

• Delay: Increasing the display rate from 1200 to 2400 baud produced no significant performance or attitude changes

• Variance: Increasing the variability of the output display rate produced a significant deterioration in both performance and attitude

Grossberg’s Experiment

• Problem Solving Context: System response time has little effect on performance

Why?

• Users simply adjust their tactics to make best use of their time on system

• Response Times in problem solving activities varied : 1,4,16 and 64

• As mean delay increased , users became more cautious and deliberate

• However, no definite effect on time required to reach solution

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Transferring to the Editing environment

• Editing a routine cognitive skill• Additional mental preparation time not

useful, in fact would interfere with the task completion time ( because of irritation )

• Experiments are always motivated to complete their tasks, but not in the real world

Editor Design Considerations

How can we make editor easy to use ?

• Depends on the– Command language of the editor– Underlying structure ( editor states or modes…)

• Tradeoff: – Our inability to learn, remember, and effectively

use large complex command setsvs

desire to achieve editing objectives within minimum time

• Limits range of design options

Many approaches

• Popular wisdom– Principle of Predictable Behavior– User Engineering Principles

• Observation– Dzida’s Questionnaire study: User perceived quality as a

multi-dimensional concept– Identified 7 major categories

• Learning Process– 1. Self teaching through trial/error with machine

feedback most effective– 2. Anxiety decreased learning

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Controlled Experiments

• Command language structure and learning ability– Whether user options are good for everyone’s

performance ?• Experiment: Two versions of editors

– Inflexible : full commands, no abbrv., extra spaces, or defaults allowed

– Flexible : lot of freedom

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Results

• Flexibility pros and cons– More prone to syntax errors– Completed tasks faster

• Role of English-similar commands– It is more helpful ?

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• Tested with two versions of same editor (NOS)– Typical Notational Syntax– Legitimate English phrases

• 24 paid subjects• English version

– Completed more tasks– Error rate was lower– Editing efficiency was better

Surface syntax of an editor is surprisingly important from human engineering point of view

Input and Output Devices

Psychological and Human factors underlying design and use of keyboards, screen displays

and pointing devices

Key Entry

• The most common means of encoding letters and numbers

Keyboard Devices

Oldest typewriters Teletypewriters Electric typewriters

Detailed research exists in keyboard design ?

Detailed research exists in keyboard design

• Keyboard layout (e.g. QWERTY)• Numeric keys• Standard Key size• Slope of keyboard• Key depression force required• Key displacement• Type of Kinesthetic feedback from key

actuation

Typing speed

• Some factors– Finger ballistics– Reaction time– Motor learning– Short term memory– Human information processing capacity

• Average single finger tapping rate: 6 keys/s

Little finger Index Finger = 20% increase

Some interesting stats

• Good typists: 0.2 secs per keystroke ( 50 words/min)

• Less Frequent users: 0.7 secs• Experienced Typists: 0.08 secs (12 taps/sec)• Typing with alternate hands: 25% faster than

with one hand

Control the necessary echo output rate for a display

Effects of Training

• Poor typing habits are difficult to shed• Self-taught typists do not reach even half the

speed expected from entry level typists

• Worth considering the benefits of specialized training

The Shaffer and Hardwick Experiment

• Limitation of human information processing capabilities

• Material:– Difficult but coherent text– Randomly selected words– Short words of Random character sequences

• Explanation– “Acquisition of a hierarchy of habits” ( ability to type a

whole word as a single unit)– Able to read farther ahead, as opposed to random

characters

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main() { unsigned paddr,pdata; LOOP: printf("Input port address (hex): "); scanf("%x",&paddr); pdata = inp(paddr); printf("Port(%xh) = %xh\n",paddr,pdata); goto LOOP; return 0; }

0.159 secs per keystroke

0.162 secs per keystroke

More than double the time

Error rates

• Error rates vary much from operator to operator than does speed

• Effect of visual feedback– Masking the keyboard– Masking the printed text

•reduces the speed and accuracy•Error : 0.9% 2.6 %•Speed : 30%

•reduces only the accuracy•Error : 40% increase !

Other studies

• Signaling errors immediately is helpful ( 25% faster)

• Automatic error correction: many editors incorporate it

Conclusions

• Lot of scope for studies of human factors aspects of the use of editors for searching , inspecting and maintaining file systems using interactive text-editors

• Many research areas exist(ed)– Underlying model of information structure– Techniques for selecting small segments of text– Form of editor commands– 2-D editors vs 1-D editors– Error feedback and benefits of automatic error correction– Split-screen and multiple-screen editing operations– Screen size and material exposed to user– Color Displays– Audio Input, audio feedback– Direct use of eye movement for pointing and menu selection