Psychophysical experiments have shown that human heading judgments can be biased by the presence of moving objects. Here we present a theoretical argument that motion differences can account for the direction of bias seen in humans. We further examine the responses of a computer simulation of a model for computing heading that uses motion-opponent operators similar to cells in the primate middle temporal visual area. When moving objects are present, this model shows similar biases to those seen with humans, suggesting that such a model may underlie human heading computations.