CS 851: Forensic Software Engineering

Human Error by James Reason

Chapter1:The nature of error

Chapter2:Studies of human error

RAJAT TIKOO18th October, 2002

The nature of error

Reason opens with examples of accidents caused due to human error:

• Three Mile Island (1979)

• Bhopal Gas Tragedy (1984)

• Challenger mission (1986)

• Chernobyl disaster (1986)

• Others….

• “Knowledge and error flow from the same mental sources, only successes can tell the one from the other.” (Mach, 1905)

Cognitive balance sheet

• The underlying theme:

“Correct performance and systematic errors are two sides of the same coin.”

• A knowledge base that contains specialized theories preserves meaning, yet can lead to confirmation bias.

• Errors involved in boiling an egg?

• But (in reality) human error is neither abundant nor as varied as its vast potential might suggest.

• Are errors predictable?

Variable and Constant errors

Intentions, actions and consequences

Was there a prior intention to act?

If No, was there intention in the action ?

If no, then involuntary/non-intentional action

else spontaneous/subsidiary action

If Yes, did the actions proceed as planned?

If no, unintentional action (slip/lapse)

If yes, did the actions achieve their desired end?

If no, intentional but mistaken action

If yes, successful action

Error: working definitions

• Errors: planning failures (mistakes) and execution failures (slips and lapses)

• “Error will be taken as a generic term to encompass all those occasions in which a planned sequence of mental or physical activities fails to achieve its intended outcome, and when these failures cannot be attributed to the intervention of some chance agency.”

• Slips and lapses are errors which result from some failure in the execution and/or storage stage of an execution sequence, regardless of whether the plan which guided them was adequate to achieve its objective.

Error: working definitions

• Mistakes may be defined as deficiencies or failures in the judgmental and/or inferential processes involved in the selection of an objective or in the specification of the means to achieve it, irrespective of whether or not the actions directed by this decision scheme run according to plan.

• Thus, mistakes are likely to be more subtle, more complex and less well understood than slips.

• Comments on this definitions?

Classification of errors

• Behavioral level of classification (What?)

Errors are classified according to some observable features of the erroneous behavior (omission, repetition, reordering).

• Contextual level of classification (Where?)

Why did the error occur at a particular position in a particular behavioral sequence?

• Conceptual level of classification (How?)

Based on the assumptions about the cognitive mechanisms involved in error production.

Error Types

• A sequence of action has three stages: planning, storage and execution.

Cognitive Stage Primary error type

Planning Mistakes

Storage Lapses

Execution Slips

Methods of investigating error

• Naturalistic methods or “corpus gathering”

• Questionnaire studies

• Laboratory studies

• Simulator studies

• Case studies

• Comments/ Questions?

Chapter 2: Studies of Human Error

Early psychological observers of human error:• Sully’s Illusions (1881)

“Any species of error which counterfeits the form of immediate, self-evident or intuitive knowledge, whether as sense-perception or otherwise”

• The Freudian slip (1896)“…he became convinced that all of these normally inconsequential slips and lapses betrayed the presence within the unconscious of repressed impulses.”

• Meringer and speech errors (1895)

Chapter 2: Studies of Human Error

• The Gestalt tradition (1912)

Holistic view to physiological phenomena

• Lashley and Head (The neurophysiologists) (1917-1920)

How is relatively automatic performance characteristic of skilled or highly practiced behavior achieved?

• Bartlett (1932)

Used the notion of schema to explain systematic errors

Chapter 2: Studies of Human Error

• Bartlett (1932)

A schema is “an active organization of past reactions, or of past experiences, which must always be supposed to be operating in any well-adapted organic response. That is whenever there is any order or regularity in behavior, a particular response is possible only because it is related to other similar responses which have been serially organized, yet which operate, not simply as individual members coming one after another, but as a unitary mass.”

The natural science tradition

• Focused attention and bottleneck theories

Is there a bottleneck in information processing by humans?

i.e. at what stage does a parallel processing system, capable of handling several inputs at the same time, become transformed into a serial system through which only one set of signals could be handled at any given moment?

-Dichotic listening

• Contradictory views

The natural science tradition

• Divided attention and resource theories

Subjects asked to distribute their attention between the assigned activities and to deal with them to the best of their ability.

Interference can occur – the main interference can occur when the two tasks compete for the same functions.

• Multichannel processor theories

advocates against the above which assume the existence of a GPLCCP.

The natural science tradition

• Allan Allport (1980)

“In general, we suggest, any complex task will depend on the operation of a number of independent, specialized processors, many of which may be common to other tasks.”

• Properties of primary memory

• STM (Short Term Memory)

• e.g. remember a larger number like 196443404412,

• Easier to remember in chunks

• Immediate memory span ~ 7 items

The natural science tradition

• Concept of working memory (1974 - )

• Derived from STM

• A central executive (capacity control resource)

• 2 slave systems:

Articulatory loop

Visuospatial scratchpad

• There is a competition between resources needed to preserve temp. data generated during processing and those consumed by the processing itself.

The Cognitive Science tradition

• Contemporary schema theories

data structures for representing concepts stored in memory.

• The Norman-Shallice model

horizontal and vertical threads

• Subjective Utility Theory

• Reluctant rationality

Cognitive Strain and Persistence forecasting

The Cognitive Science tradition

• General Problem Solver (GPS)Problem behavior graph

• Rouse’s “fuzzy rule” modelDerived from GPS

• Ramussen’s frameworkskill-based, rule-based and knowledge based levels

• Parallel Distributed Processing (PDP)

• Global Workspace (GW) model

Conclusions

• Common themes/principles

• Controlled Processing vs Automatic Processing

• “The price we pay for this largely automatic processing of information is that perceptions, memories, thoughts and actions have a tendency to err in the direction of the familiar and the expected.”