Abstract
It is widely believed that persistent neural activity underlies short-term memory. Yet, as we show, the degradation of information stored directly in such networks behaves differently from human short-term memory performance. We build a more general framework where memory is viewed as a problem of passing information through noisy channels whose degradation characteristics resemble those of persistent activity networks. If the brain first encoded the information appropriately before passing the information into such networks, the information can be stored substantially more faithfully. Within this framework, we derive a fundamental lower-bound on recall precision, which declines with storage duration and number of stored items. We show that human performance, though inconsistent with models involving direct (uncoded) storage in persistent activity networks, can be well-fit by the theoretical bound. This finding is consistent with the view that if the brain stores information in patterns of persistent activity, it might use codes that minimize the effects of noise, motivating the search for such codes in the brain.
Highlights
Short-term memory, which refers to the brain’s temporary buffer of readily usable information, is considered to be a critical component of general intelligence (Conway et al, 2003)
We have provided a fundamental lower-bound on the error of recall in short-term memory as a function of item number and storage duration, if information is stored in graded persistent activity networks
This bound on performance with an underlying graded persistent activity mechanism provides a reference point for comparison with human performance regardless of whether the brain employs strong encoding and decoding processes in its memory systems
Summary
Short-term memory, which refers to the brain’s temporary buffer of readily usable information, is considered to be a critical component of general intelligence (Conway et al, 2003). We restrict ourselves to obtaining limits on short-term memory performance purely due to noise in persistent activity networks, if analog information is stored directly into these networks, or if it is first well-encoded to make the stored states robust to ongoing noise. Short-term memory experiments quantify the precision of memory recall. In such experiments, subjects are briefly presented with sensory inputs, which are removed. Persistence can be limited, though forgetting over time is a less severe constraint than capacity: several experiments show that recall performance declines with delay
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