Lecture on Face Perception, Methods, and Experimental Design

Overview

• Recap from last week: dual focus on questions about face perception in the brain and cognitive neuroscience methods.
• Today's focus: TMS (Transcranial Magnetic Stimulation) and animal studies.

Behavioral Methods

• Good for characterizing internal representations (e.g., face inversion effects).
• Major disadvantage: sparse data, challenging inference of mental processes based on output alone.

Functional MRI (fMRI)

• Best spatial resolution for normal subjects.
• Poor temporal resolution and limited in determining causal neural activity.
• Importance of understanding causality in experiments.

Causality in Brain Activity

• Concept: if X causes Y, Y wouldn't happen without X or happens more with X.
• Types of causality: stimulus→neural activity (testable with fMRI) vs. neural activity→behavior (challenging with fMRI).

Temporal Resolution of fMRI

• BOLD response is delayed and sloshy (~5-6 seconds after stimulus).
• Contrast with neural activity measured in milliseconds (e.g., V1 visual cortex activity).

Electrophysiological Methods

• ERPs (Event-Related Potentials) & Magnetoencephalography (MEG): excellent temporal resolution, poor spatial resolution.
• Direct brain recording: good space/time resolution but very invasive.

Studying Patients with Brain Damage

• Strong causal link between brain regions and behaviors (e.g., double dissociations: face recognition vs. object recognition).
• Example: electrical stimulation in fusiform face area causing hallucinatory face perception.

Transcranial Magnetic Stimulation (TMS)

• Non-invasive method to disrupt brain regions in normal subjects.
• Procedure: coil next to head, strong/brief current, induces electric field affecting neural activity.
• Example study setup: TMS on occipital face area during a face matching task.

TMS: Advantages and Limitations

• Provides causal evidence for brain regions in perception/behavior.
• Good temporal information, but moderate spatial resolution and depth limitation.
• Application examples: zapping occipital face area, vertex as a control site.
• Findings: TMS can alter accuracy in face perception tasks.

Role of Animal Studies

• Address questions human methods can't (e.g., neural code, developmental wiring, anatomical connections).
• Ethical considerations: regulated care, pain avoidance, quality of lab life vs. nature, long-term benefits of research.

Fascinating Animal Research Methods

• Recordings and experiments in primates (e.g., face patches in monkey brains).
• Visual stimuli responses: detailed neural coding of faces.
• Tracking changes over time and development.
• Analyzing anatomical connections and stimulus effects.

Experimental Design Considerations

• Independent vs. dependent variables.
• Importance of precise predictions and avoiding confounds.
• Creating minimal pairs in task designs to isolate mental processes.
• Details to consider: task engagement, baseline conditions, run organization, and condition allocation.

Group Activity on Experimental Design

• Discussed control conditions for snake perception studies (snakes vs. horns, worms, garden hoses).
• Importance of task engagement to avoid subject inactivity.
• Baseline condition usage for clearer data interpretation.
• Practical setup: concatenated runs, conditions allocation, and subject-task interaction.

Summary

• Emphasis on methodology's pros and cons for studying brain-behavior relationships.
• Experimental design: balance between scientific rigor and practical feasibility.
• Preview of further discussions and remaining materials.