Lesson 2: Human Abilities and Cognition

Human abilities impose limits on interface design. For example, short-term memory can only hold about 7±2 chunks of information. An overloaded screen forces users to remember too much, causing errors. HCI teaches techniques like "recognition rather than recall" – for instance, using menus or icons so users don't have to memorize commands. Human perception is also limited: small fonts or low contrast are hard to read. Designers must use clear fonts, sufficient color contrast, and simple layouts. Understanding perception (color vision, attention) helps you predict how users perceive your interface.

Cognitive load refers to how much mental effort a user needs. High load causes frustration. Good interfaces break tasks into steps and use progressive disclosure (show only what's needed). For example, in an online form, grouping related fields and using checkboxes instead of asking users to list items helps reduce cognitive load. HCI also addresses physical factors: Fitts' Law tells us that the time to tap a target is based on its size and distance. This means smartphone buttons should be large enough and placed within easy thumb reach. Keeping mental and physical loads low is a key design principle.

Ready to apply this? The practice set below walks through exam-style problems with step-by-step solutions and an interactive quiz.