Formal Models of Memory

Occam’s razor

All else being equal, accept the simpler of two or more explanations

Model:

a formal (often mathematical) description of a theory that makes specific, testable predictions

• More precise than verbal descriptions

• Assumptions are made explicit

Threshold model

Key Idea: when a memory exceeds threshold, it is retrieved

there is a threshold of activation that a memory trace must exceed for it to be identified as “old” (or recognized). there may also be some threshold below which information is clearly identified as “new.”

Generate-Recognize model

Key Idea: Recall = (1) generate possible responses + (2) recognize;

Recognition = recognize only

recall is a two stage process process

Network models

associative structures, memory as a collection of associations

Global matching models

memory accessed as a whole. memories are accessed through processes that consider the entire set of traces available. structure emerges as a function of retrieval, not long-term storage.

Parallel distributed models

biologically inspired (nervous system like), a neuron contributes to the representation of many memories. networks consisting of highly interconnected nodes. pattern of activation across nodes represents information.

Dual process models

assumes two types of memory processes

catastrophic forgetting

old memories get “overwritten”

familiarity

information identified as old when it exceeds some threshold. captured in most formal models of memory.

recollection

conscious retrieval of associated information

spatial memory

supports out ability to navigate, locate things in the environment, estimate distances & directions, etc.

temporal memory

allows us to estimate when something occurred - with respect to the present, other events, absolute time

place cells

hippocampal cells that

respond to a particular part

of space

grid cells

entorhinal cortex cells

activate in the pattern of a

“grid” of equilateral triangles

boundary cells

hippocampal cells that

activate at the boundary of

an environment

time cells

hippocampal cells active as

a function of time on the

treadmill

Parahippocampal Place Area (PPA)

neocortical regions active during scene perception

place cells

single unit recording in humans revealed place-selective (in hippocampus) and landmark-selective cells

hit

correct recognition of old memory

miss

old item’s activation level fails to reach the threshold, it is rejected, failing to recognize old item

correct rejection

new item is rejected because the memory does not exceed threshold (because it is new)

false alarm

new item falsely identified as old, if it has representation in memory that exceeds threshold

what happens during “generate” part of generate-recognize model?

people take the available retrieval cues to generate a set of memory traces whose contents can be reported. this is done by activating information in memory that is associated with the cues, then information that is associated with that, and so on