Comparing a visual memory with new visual stimuli can bias memory content, especially when the new stimuli are perceived as similar. Perceptual comparisons of this kind may play a mechanistic role in memory updating and can explain how memories can become erroneous in daily life. To test this possibility, we investigated whether comparisons can produce other types of memory distortion beyond memory bias that are commonly implicated in erroneous memories (e.g., memory misattribution). We hypothesized that the type of memory distortion induced during a comparison depends on the perceived overlap between the memory and incoming stimulus—when the input is perceived as similar, it biases memory content; when perceived as the same, it replaces memory content. Participants completed a delayed-estimation task in which they compared their memories of color (Exp.1) and shape stimuli (Exp.2) to probe stimuli before reporting memory content. We found systematic errors in participants’ memory reports following perceived similarity and sameness that were towards the probes and larger following perceived sameness. Simulations confirmed that these errors were not explained by noisy encoding processes that occurred before comparisons. Instead, computational modeling suggested that these errors were likely explained by probabilistic replacement of the memory by the probe following perceived sameness and integration between the memory and the probe following perceived similarity. Together, these findings suggest that perceptual comparisons can prompt distinct forms of memory updating that have been described previously and may explain how memories become erroneous during their use in everyday behavior.