Methods in Cognitive Science - PDF

Methods Reaction Time (RT) RT as a function of processing complexity - How much time do (complex) mental processes take ❖ The longer the time, the more complex the mental process is - i.e. lexical decision: ❖ RT is a function of morphological complexity - Blueberry faster than...

Methods Reaction Time (RT) RT as a function of processing complexity - How much time do (complex) mental processes take ❖ The longer the time, the more complex the mental process is - i.e. lexical decision: ❖ RT is a function of morphological complexity - Blueberry faster than elephant - Blueberry faster than strawberry ❖ RT is a function of Word frequency - Book faster than cook ❖ Many variables change the complexity of a word - Cross-modal priming ❖ Visual lexical decision ❖ Sentence/auditory stimulus presentation ❖ Visual target related to some word in the sentence ❖ Equation for Priming: RT to related words - RT to unrelated words = PRIMING EFFECT - Rapid Categorization ❖ Visual category decision ❖ Accuracy + time = reveal info about object ❖ Stimulus presentation: minimal amount of time required to perceive TRADITIONAL COGNITIVE METHODS - RT (simple, primed) - Recall - Recognition - Neuroscience methods - Combinations *** (better) Eye tracking - precise timing, spatial resolution - Measures ongoing processes as evidenced by eye movements - Used mostly in language, vision, and attention - Eye movements to: ❖ Get clearer image (fovea) ❖ Get coherent picture (visual routines) ❖ Tracking objects (pursuit) ❖ Attend to “attention grabber: (features) - Involuntary saccades ❖ Serve intentions and actions - voluntary saccades Scan paths and fixations - where the eye goes and how long under different conditions Development of face perception - eye movements linked to development of visual acuity Eye movements as “window” to into the minds work: - scan paths and fixations are correlated with perceptual and cognitive processes ❖ Delays suggest difficulty (complexity) ❖ Regression suggest revision Fixation duration - time spend on particular regions (longer = more difficult) Saccade length - how long was saccade A-B (shorter = more difficult) Regressions - rereading patterns (more regressions = more difficult) ❖ Literal interpretation trumps metaphorical ones Cognitive Neuroscience Methods - Signals from direct neuronal activity (good timing, bad spatial) ❖ Single cell recordings - Micro-electrodes inserted into the brain - Activity of single cells (~1ms) as a function of stimulus id detected by the electrode - Recording of APs in response to a stimulus ❖ Recording pattern of firing - Can show specialization of neurons/regions ❖ ERP ❖ MEG - Signals arising from increase in blood flow in active tissue (bad timing, good spatial) ❖ PET ❖ fMRI - Lesions Neuronal coding & concepts Neurons that respond to single visual features Neurons in the IT that responds to complex objects (faces, hands, etc.) Neurons can be specialized for faces, hands, places, motion, wavelength, etc. A neuron in the hippocampus responds to particular token stimuli regardless of mode of representation (faces, names) The same neuron also fires in response to the spoken name Event-related Potentials (ERPs) Measure post-synaptic activity related to stimuli presentation Electrical activity on the scalp is recorded during repeated events Brain waves are then segmented and averaged Recordings of large groups of neurons Pattern of waves associated with cognitive events i.e. N400 (negative peak at 400ms post stimulus) Semantic anomaly “Surprise effects” P600 (positive peak at 600 ms) Structural anomaly P100 visual processing LIMITATIONS: Limited spacial resolution, despite high temporal resolution Requires many trips Skull & brain tissue distort electrical fields MEG Measures magnetic fields resulting from cortical activity Patter of waves associated with particular events 100,000 neurons recording i.e. m170: 170ms - response to words i.e. m250: 250 ms - word meanings LIMITATIONS Expensive to keep the SQUID cool Requires the participant to maintain a potentially uncomfortable body position for long durations The technology and analysis are relatively new and complicated PET fMRI Measures changes in hemoglobin (iron-rich proteins in red blood cells) as a function of neuronal activity Increase in neuronal activity is accompanied by decrease in deoxygenated hemoglobin (more magnetic) and increase in oxygenated hemoglobin (less magnetic)  A magnet is used to “align” the protons in deoxygenated blood; a radio wave disrupts this alignment (resonance) the difference in magnetism is picked up by the scanner The regions most active produce the highest contrasts over time; BOLD: Blood Oxygen-Level Dependent contrast Activation areas are measured in “voxels” (volumetric pixels) units of space (about 1-33 mm); contiguous voxels (about 50) signals greater area of activity fMRI provides a non-invasive, indirect measure of brain activity Event-Related fMRI Type of fMRI design Compares activity for discrete events, allowing for: Fast-paced designs More realistic event ordering Post-hoc binning of individual trials Example fMRI: Acquisition of a 2nd language (L2) Bilingualism: Acquisition Age: Early L2 Late L2 Monitored: Broca’s & Wernicke’s areas Measure: difference in centre-of-mass (of a cluster) between significant areas LIMITATIONS More expensive than ERP and PET poor temporal despite good spatial resolution (still better than PET) Provides only an indirect measure of brain activity p Distortions in some brain regions Noise from the scanner can be distracting May be uncomfortable for claustrophobics Participants must remain still, limiting response types and experiment duration Problems with fMRI analysis Everything is activated... but some spots reach a “threshold” Threshold level is often arbitrary Activation level of voxels (“t-level”) Number of contiguous voxels (50? 49?) Only some activated spots are reported (ROA/ROI) Often activated spots are not of theoretical relevance, but they might be A lot goes unreported or unaccounted for Dissociations Single dissociation: when a lesion to brain area X impairs the ability of a patient to do task A but not task B brain area X and task A are associated brain area X and task B are dissociated Double dissociation: when damage to area X impairs the ability to do task A but not task B, and damage to area Y impairs the ability to do task B but not task A 2 areas have complementary processing STM AND LTM DISSOCIATION Functioning STM but cannot form new LTM’s Clive Wearing H.M. Poor STM but functioning LTM K.F. Overview of Methods  Experimental techniques used in cognitive science (and neuroscience) employ diverse measures of activity: RT (from button press to eye movements) Electrical activity: ERP, MEG, TMS Blood flow: PET, fMRI Study of brain lesions also informative Techniques have different sensitivities **Best approach: multiple techniques aiming at convergence of results