Unit 4: Memory 5.2.16
Part 4 Storage
Working/Short-term Memory Memory Storage Storage is at the heart of memory 3 types of memory storage: Info Unconscious processing Sensory Memory New & important information consciously encodes Long-term Memory Working/Short-term Memory Encoding Retrieving
Sensory Memory R G T F M Q L Z S George Sperling (1960) Showed participants 3 rows of letters for only 1/20th of a second People can recall only about half of them (RTMZ) The exposure time for the stimulus is so small that items cannot be rehearsed.
Sensory Memory R G T F M Q L Z S When given cues to focus only on one row at a time, people can recall all the letters, but only momentarily Iconic memory: a momentary sensory memory of visual stimuli; a photographic or picture-image memory lasting no more than a few tenths of a second
Sensory Memory Echoic memory: a momentary sensory memory of auditory stimuli; if attention is elsewhere, sounds & words can still be recalled within 3 or 4 seconds The duration of sensory memory varies for the different senses. Iconic 0.5 sec. long Echoic 3-4 sec. long Hepatic < 1 sec. long
Sensory Memory
Working/Short-term Memory Working memory, the new name for short- term memory, has a limited capacity (7 +/- 2) and a short duration (20 seconds). Without active processing, memories have a limited life Recall is slightly better for numbers than letters Using chunking, but no rehearsal, average person retains only about 4 chunks in short- term memory Main idea: at any given moment, we can consciously process only a very limited amount of information
The Magical Number Seven, Plus or Minus Two Ready to test it? M U T G I K T L R S Y P You should be able to remember 5-9 letters
Long-term Memory Our capacity for storing long-term memories is essentially limitless Computers have the ability to beat our brain’s capacity to remember literal text, but given the number of brain synapses, “the total memory capacity of all computers in the world is less than that of a single brain” Rajan Mahadevan
Long-term Memory
Memory Stores Feature Sensory Memory Working Memory LTM Encoding Copy: sight/photographic Phonemic: sound of the words Semantic: meaning of the words Capacity Unlimited 7±2 Chunks Very Large Duration 0.25 sec. 20 sec. Years
Storing Memories in the Brain Memories do not reside in a single spot in our brains Using rats, Lashley (1950) suggested that even after removing parts of the brain, the animals retain partial memory of the maze. Forgetting occurs as new experiences interfere with our retrieval
Synaptic Changes Neuroscientists are focusing on synapses to find the physical basis of memory Memories begin as impulses whizzing through brain circuits; leaving permanent neural traces Where does the neural change occur? Clues point to the synapses (where nerve cells communicate with one another) With increased activity, neural interconnections form and strengthen
Synaptic Changes Studies of the sea snail Aplysia showed an increase in releasing the neurotransmitter serotonin after conditioning Serotonin increases the efficiency of transmitting signals between the affected synapses, which leads to more efficient neural circuits Long-term potential: an increase in a synapse’s firing after brief, rapid stimulation. Believed to be a neural basis for learning & remembering
Synaptic Changes Electron microscope images show just one receptor site (gray) reaching toward a sending neuron (red) before long-term potential (top) and two receptor sites afterward (bottom). A doubling of receptor sites means that the receiving neuron has increased sensitivity for the neurotransmitter molecules released by the sending neuron
Synaptic Changes After LTP has occurred, passing current through the brain won’t disrupt old memories, but will wipe out recent memories Electroconvulsive therapy for depressed people can wipe out recent memories Blow to the head has the same effect
Stress Hormones & Memory Stress hormones produced when excited/stressed make more glucose to fuel the brain, signaling that something important has happened Amygdala (brain’s emotion processing center) boosts activity in the brain’s memory-forming areas Stronger emotional experiences = stronger, more reliable memories
Implicit & Explicit Memories Amnesia: the loss of memory Implicit memory: retention independent of conscious recollection Explicit memory: memory of facts and experiences that one can consciously know & “declare” We have two different memory systems going on, implicit and explicit. Some people with brain damage cannot consciously recognize faces, but will have a physiological response to seeing a familiar face, demonstrating an unconscious recognition. Even Alzheimer’s patients whose explicit memories for people & events are lost display an ability to form new implicit memories.
Hippocampus Hippocampus – a neural center in the limbic system that processes explicit memories Brain scans capture activity in the hippocampus when brain is forming a memory & when recalling words Damage to the hippocampus disrupts some types of memory: birds cannot return to places where they have stored food if their hippocampus is removed; damage to the left hippocampus impairs ability to remember verbal info, but not visual designs or locations & vise-versa; loss of hippocampus means a loss of recent memories (within a month) but not older memories
Anterograde Amnesia After losing his hippocampus in surgery, patient Henry M. (HM) remembered everything before the operation but cannot make new memories. We call this anterograde amnesia. Memory Intact No New Memories Surgery
Cerebellum Cerebellum – a neural center in the hindbrain that processes implicit memories.
Dual Memory System Explicit-implicit system explains infantile amnesia: reactions & skills we learn during infancy stay with us, yet as adults we recall nothing (explicitly) of our first 3 years We index much of our explicit memories with words nonspeaking children have not yet learned The hippocampus is one of the last brain structures to mature
Crash Course Psychology Episode 13: How We Make Memories