Perception Lecture Recording on March 11th 2025

Attention and the Attentional Blink

• Attentional Blink: A phenomenon where a short period follows the detection of a target in which another target is less likely to be noticed.

  • It's an internal process that occurs after identifying a target, impacting sensitivity to subsequent targets.

  • The time window for this effect is approximately 500 milliseconds.

Repetition Blindness

• A related phenomenon similar to the attentional blink:

  • Not only is the second identical target not detected, but it may also result in a failure to consciously report it.

Rapid Serial Visual Presentation (RSVP) Paradigm

• Method used to study the attentional blink and repetition blindness:

  • Involves presenting letters rapidly, one after the other (often for only 15 milliseconds each).

  • Participants must respond to specific targets amidst distractors, assessing their ability to detect targets based on timing and their previous interaction.

  • Example targets: white font letters and the letter 'x'.

Brain Regions Involved in Attention

Frontal and Parietal Cortex

• Frontal Cortex: Associated with the Executive Attention Network, involved in controlling attention by:

  • Deciding task relevance.

  • Inhibiting irrelevant stimuli.

• Parietal Cortex: Involved in the Orienting Network, permitting visual-spatial attention and visual search.

Clinical Conditions Related to Attention Control

• Hemispatial Neglect: A condition that arises from damage to the right parietal cortex, resulting in unawareness of the left visual field despite intact vision.

• Simultagnosia: Characteristic of bilateral parietal cortex damage, where patients can only attend to one object at a time.

Neuronal Function and Selective Attention

Evidence from Neuroscience

• Studies using Moran and Desimone's work on neurons in area V4:

  • Demonstrate that attention affects how neurons fire in response to stimuli within their receptive fields.

  • Neurons only accurately reflect attended stimuli even when unattended stimuli are present.

Biased Competition Theory

• Suggests that multiple objects in a receptive field compete for the neuron's representation, and attention allows for the accurate representation of only the attended object.

Visual Attention and Brain Activation

Visual Processing Related to Attention

• Visual processing is contralateral: Left visual field processed by the right visual cortex and vice versa.

  • When attention is directed to the right visual field, left visual cortex activates and vice versa.

Olfactory System

Basics of Olfaction

• Odor: The perception produced by odorants, which are volatile molecules.

• Two pathways for odor detection:

  • Orthonasal Pathway: Odors entering through nostrils.

  • Retronasal Pathway: Odors that enter through the mouth.

Olfactory Anatomy

• Olfactory Epithelium: Contains olfactory receptor neurons (ORNs) responsible for detecting odors.

  • Bowman's glands produce mucus to trap and dissolve odorants.

  • Approximately 20,000,000 ORNs in humans.

Mechanism of Odor Detection

• G-Protein Coupled Receptors (GPCRs): Receptor proteins on ORNs that initiate the detection of odorant molecules via a lock-and-key mechanism.

• Humans possess around 350 active olfactory receptor genes, allowing detection of vast numbers of odors (estimates up to 10 billion).

Processing and Memory of Odors

• The olfactory tract transmits odor information to:

  • Piriform Cortex: Primary olfactory cortex.

  • Amygdala: Associated with emotional responses to odors.

  • Hippocampus: Important for memory formation related to odors.

• Unique to olfaction: No need to pass through the thalamus.

Adaptation and Sensitivity to Odors

• Adaptation: The decrease in sensitivity to an odor after prolonged exposure.

  • Cross-adaptation: Reduced sensitivity to similar odors based on previous exposure.

• Odor identification improves with context, emphasizing the importance of associations for recognizing odors.