Notes

Overview:

This lesson seeks to help students:

1. Describe the major elements of the perceptual process
2. Identify the main factors that influence what individuals perceive

Perception

• Perception is the process by which people select, organize, interpret, and respond to information from the world around or within them.
• Perception is the selection and organization of environmental stimuli to provide meaningful experiences for the perceiver.

• The perceptual process consists of the following elements:

  • Environmental stimuli

    • People receive stimuli from the environment through their (5: Sight, Hearing, Taste, Touch, Smell) senses when they observe their environment.

  • Observation

  • Perceptual selection

    • When the stimuli are received a person might pay attention to some of the aspects in the environment and ignore others. This filtering out of most information to deal with the most important matter is referred to as selective screening.
    • The influencing factors are due mainly to external and internal factors.
    • External factors are:
      • Size
      • Intensity
      • Contrast
      • Motion
      • Repetition
      • Novelty and Familiarity
      • A combination of the above may be operating at any time to affect perception.
    • Internal factors are:
      • Personality - personality is a strong influencing factor in determining how an individual perceive (e.g., other people).
      • Learning - affects perception by the development of perceptual sets. A perceptual set is an expectation of a particular interpretation based on past experience with the same or similar objects.
      • Motivation - the urgent needs and desires at any particular time can influence perception.

  • Perceptual organization

    • The process by which people group environmental stimuli into recognizable patterns.
    • Perceptual grouping is the tendency to form and perceive objects as a continuous pattern (Law of Continuity).
    • Closure is the tendency to complete an object and perceive it as a constant (Law of Closure).

  • Interpretation (Understanding what you are looking at...)

  • Response (Optional...)

Attention

"Everyone knows what attention is. It is the taking possession of the mind, in clear and vivid form, of one out of what seem several simultaneous possible objects or trains of thought. Focalization, concentration of consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others, and is a condition which has a real opposite in the confused, dazed, scatterbrain state..." - William James (1890).

Attention is what enables us to process information about the world around us. We can only be aware of things around us if we pay attention to them. We can think of attention as a spotlight that we shine on things in the world around us to make them stand out. When something "stands out", we notice it, bringing it into our awareness, and then process or interpret it. Attention can change rapidly, switching from one thing to another. It can be steered by our intentions ("top-down"), as when we look for a particular face in a crowd, or it can be steered by features of objects in the world ("bottom-up"), as when our attention is grabbed by a police car's flashing lights in our rearview mirror. Pre-attentive processes help us decide what to pay attention to and what to filter out and ignore. Attention filters and feeds information about the world around us into our minds.

Overt-Attention

Movements of the eyes allow selective acquisition of visual signals. Other sensory organs equally allow selective capturing of environmental signals.

Covert-Attention

Ability to focus on particular stimuli without selective acquisition guided by the changes/movement of sensory organs.

Attentional Systems

Two Orienting Mechanisms Controlling Attention

• Exogenous (reflexive)
  • Engaged by peripheral cues
  • Fast (approx. 100 ms)
  • Occurs even with uninformative cues
• Endogenous (voluntary)
  • Engaged by central cues (e.g., arrows)
  • Slower (approx. 300 ms)
  • Occurs only with informative cues

Spotlight of Attention

Helmholtz observed that we can enhance perception, if we focus our attention on a location in the visual field. However, enhancing perception in one part of the visual field takes place at the expense of other areas.

At which level of processing does Attention play a role?

Broadbent's Filter Theory

• Early selection.
• Selection is based on physical properties of the stimulus (e.g., pitch, loudness, etc...)
• Only one input channel can be processed at a time.
• Semantic interpretation only after selection.
• Conscious control.
• It takes time to shift attention.

Competing Hypotheses

• Early Selection - Broadbent (1958) proposed that physical characteristics of messages are used to select one message for further processing and all others are lost.
• Attenuation - Treisman (1964) proposed that physical characteristics are used to select one message for full processing and other messages are given partial processing.
• Late Selection - Deutsch & Deutsch (1963) proposed that all messages get through, but that only one response can be made (late selection).

Popout

Could you spot a red dot in an image full of green dots? The red dot pops out and the performance in detecting such stimulus is not affected by the increase of the "distractors". (Feature/Parallel Search)

Could you spot the bar that is "vertical and white"? this represents conjunction search because you are searching for multiple features at the same time and this type of tasks increases linearly with the number of "distractors". (Conjunction/Serial Search)

Stroop Task

Contrastive information can collide with attentional processes, such as the automatism of reading.

Effects in Early Visual Cortex

Recordings of cells in Monkey V1, measured as spikes/s under the top left conditions.

Effects of Attention

A Definition by Exclusion

![[Screenshot 2025-02-17 alle 16.57.52.pn|600]]

What can we Attend to?

• Spatially oriented attention vs. Object oriented attention.
• Popout as a pre-attentive mechanism.

Shadowing Task

Selective and Divided Attention

• Attention is studied by presenting participants with two or more stimuli at the same time.
• This is called dual-task performance.
• In selective (focused) attention tasks, people are instructed to respond to one input only.
• In divided attention tasks, people are asked to process and respond to more than one input.