A Probabilistic Palimpsest Model of Visual Short-term Memory
Figure 8
Misbinding errors when varying the proportion of conjunctive units.
These plots are based on a mixed population code recalling the orientation of one of two stored items (the correct value is indicated by the red vertical bar). There is a fixed total number of 200 units; the ratio of feature to conjunctive units increases for the graphs going from top to bottom. Left: Average (and standard deviation, shown by the penumbra) of the log-posterior distributions over orientation, given the stored memory states averaged over 1000 instantiations of the noise. If the population code only consists of feature units, the posterior comprises two equal modes the incorrect mode disappears as the fraction of conjunctive units increases. However, feature units improve the localization; as their number decreases, the widths of the posterior modes increases. Right: Distribution of 1000 sampled responses, showing how misbinding errors tend to disappear when sufficient conjunctive information is available. The red (respectively green) vertical lines indicate the target (respectively non-target) item orientation. The red Gaussian curve shows the probabilit distribution of a Gaussian distribution centred at the correct target value and with a standard deviation derived from the Fisher information of the associated population code.