Also the distribution of old and new pictures throughout the length of the block was controlled, so as to avoid response-decision bias and to maintain an equal probability of a “new” object across quartiles within a block. This type of bias refers to subjects being able to calculate predictive probabilities about the upcoming stimuli and responses, which could lead to faster reaction times and/or a drop in attention. Within a block there were 136 trials, equally divided between V, AV, V−, and V+ conditions (i.e. 34 trials each). This is identical to the block length used in our prior studies