Models of spatial reasoning often assume distinct visual and spatial representations. In particular, the visual impedance effect – slower response time when more visual details are represented in three-term series spatial reasoning tasks – has been taken as evidence for the distinctive roles of visual and spatial representations. In this paper, we show that a memory model of spreading activation based on the ACT-R architecture can explain the visual impedance effect without the assumption of distinct visual and spatial representations. Using the same memory representation, varying levels of visual features associated with an object are represented in the model. The visual impedance effect is explained by the spreading activation mechanism of ACT-R. The model not only provides a more parsimonious explanation to the visual impedance effect, but also leads to testable predictions of a wide range of memory effects in spatial reasoning.