CEN3722 Human Computer Interaction Cognition and Perception Dr. Ron Eaglin

Objectives Understand the importance of perception and cognition in HCI Describe models of cognition (cognition frameworks) Understand factors affecting perception Context Graphical Coding Color Images Depth Describe how representation influences perception

Conflicting Visual Cues Example of Poor Design Conflicting Visual Cues

Cognition Cognition refers to how we gain knowledge Objective of HCI: Understand and represent how humans and computers interact in the transmission of knowledge (paraphrased from Preece, et.al. 1996)

Understanding Cognitive Process Allow us to predict how humans will perceive, think and act. Prediction allows for design Elements of cognition Remembering Reasoning Awareness Skill development Generating (new) ideas

Stages of Information Processing Encoding Comparison Response Selection Execution Each stage takes time and this is unidirectional and sequential

Stages - Encoding Hot Flame Ouch! Encode information from environment into mental representation

Stages - Comparison Internal representation of the stimulus is compared with memorized representations stored in the brain (long-term memory)

Stages – Response Selection Deciding upon a response to coded stimuli

Stages – Response Execution Organization of response and necessary action

Stages of Information Processing

Multi-store Memory Model

Memory Model Sensory Store – External stimuli registers in modality (visual, auditory, tactile) store. Working Memory – Holds limited information for a few seconds. Long Term Memory – Holds information indefinitely, practice required for complex tasks migrating to long term.

Theories of Visual Perception Constructive theory Perception is an active process, where the world is constructed from information in the environment and previously stored knowledge. Ecological theory No active process involved – simply absorb information from the environment.

Importance of Context Adapted from Selfridge, 19955 © IEEE

Importance of Context H A Context is fundamental to interacting with computers, because it affects how we perceive objects. Context and prior knowledge allow us to interpret same symbols differently H A

Similarity Proximity Similarity Closure Continuity Symmetry

Graphical Representation May seem desirable to present information on the screen that has characteristics similar to the objects we perceive in the environment The visual system could then use the same processes that it uses when perceiving objects in the environment.

Perceptual Depth Cues Size - larger of two identical objects appears closer Interposition - a visually blocked object appears to be behind the blocking object Contrast, clarity and brightness - sharper, more distinct items appear nearer Shadows - indicate relative position Texture - more apparent in closer objects

3-D Cues

Graphical Coding Abstract systems, data objects, and other features of the interface can be represented by different forms of graphical coding Direct mappings are best: analogy in real-world Different icon sizes to reflect size of file Different line widths to represent increasing draw size Bar charts to show trends in numerical data Wastebasket to represent place for unwanted files

Color Coding Powerful way of dividing display into separate regions Useful for search tasks spotting an object in a list, but of less use for tasks requiring categorization or memorization too many colors will increase search times More effective with inexperienced users

Color Coding

Color Rules - example

Use of Color and Contrast Bad Bad OK

Icons Used to represent system objects, application tools, etc. Increasingly used at the interface for a range of systems Advantage: can reduce complexity of the system by making it easier to use Allow perceptual processes to take over. Problem: difficult to map meaning to image Especially for abstract actions: search, replace, undo, redo Concrete actions: save, print, cut, copy (?)

Lesson Summary You should now understand: The importance perception and cognition play in HCI Models of cognition (frameworks) How perception is influenced or used through Context Graphical coding Color Graphical images (icons) Perceptual (monocular) depth cues