Input-Output channels

Notes

Study Notes

HCI Notes: Input/Output Channels

Human Input-Output Channels

Detailed notes on how humans interact with and receive information from computer systems.

1. Overview of the Human Processor

The human body acts as a processor, taking in information via sensory **Input Channels** and performing actions via **Output Channels** (Motor System). This process is mediated by cognitive functions.

2. Input Channels: Receiving Information

👁️ Vision (Primary Input)

The primary sensory channel in HCI. Visual information is processed via the **retina** and sent to the visual cortex.

  • **Acuity:** The ability to see fine detail (important for reading small text).
  • **Flicker Fusion:** Rapid changes (e.g., refresh rates) appear continuous above a certain frequency.
  • **Color Perception:** Highly effective for grouping, alerting, and coding, but consider users with color blindness.
  • **Depth Perception:** Relying on cues like relative size, motion parallax, and stereopsis (key in AR/VR).

👂 Audition (Secondary Input)

Used for non-visual feedback, alerts, and context when visual attention is elsewhere (e.g., system errors, background notifications).

  • **Pitch and Loudness:** Crucial for distinguishing between different types of alerts.
  • **Sound Localization:** The ability to determine the source direction (important in 3D audio interfaces).
  • **Speech Recognition:** Used increasingly for command input (VUI).

🤚 Haptic/Tactile Input

Perception through skin (tactile) and body position/movement (kinaesthetic).

  • **Tactile:** Sensing pressure, temperature, and pain (used in touchscreens and haptic feedback devices).
  • **Kinaesthetic:** Sensing limb position and movement (critical for muscle memory in typing or using a joystick).

3. Output Channels: Performing Actions

💪 Motor System

The human motor system executes responses based on cognitive decisions. This is governed by the brain and involves the musculoskeletal system.

  • **Limb Movement:** Used primarily in HCI for device manipulation (mouse, keyboard, joystick, touchscreen).
  • **Reaction Time:** The time between a stimulus (input) and the initiation of a response (output). Composed of:
    • **Perception Time** (sensory input)
    • **Cognition Time** (decision making)
    • **Motor Time** (executing the muscle command)
  • **Speed-Accuracy Tradeoff:** A fundamental principle; trying to move faster often leads to more errors (addressed by laws like Fitts's Law).

4. Implications for Interface Design

Multimodal Design

Designing systems to use multiple channels simultaneously (e.g., visual display *and* auditory feedback) to improve effectiveness and cater to different situations (e.g., a noisy environment requiring visual, or a dark room needing audio).

Ergonomic Considerations

Designing physical interfaces (keyboards, mice, VR controllers) to fit human motor capabilities to prevent fatigue, strain, and repetitive stress injuries.

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