Sutton-Barto (SB) model of learning is based on a neuron-like adaptive element. The
model has computational features suitable for describins a variety of classical conditioning phenomena, including blocking, conditioned inhibition, and higher-order conditioning. However,
it presently does not describe within-trial phenomena related to conditioned response (CR)
topography. W e here describe in detail an extension of the SB element, referred to as the
Sutton-Barto-Desmond (SBD) model, which is capable of simulating topography of the conditioned nictitating membrane response (NMR) of the rabbit. The SBD model places certain
constraints on the SB modePs parameters and makes some additonal assumptions about the
form of inputs to the element. The model describes (1) the gradually increasing amplitude of
the C R within a trial with the peak amplitude at the temporal locus of the US, (2) the decrease
in C R onset latency over training, and (3) appropriate interstimulus interval (ISI) functions, with optimal learning occurring with an ISI of .25 seconds. In addition, the model lends itself to descriptions of neuronal firing related to the CR. W e believe the S B D model may have implications for neurobiological studies of learning and memory.