The frequency at which a stimulus is presented determines how it is interpreted. For example, a repeated image may be of less interest than an image that violates the prior sequence. This process involves integration of sensory information and internal representations of stimulus history, functions carried out in higher-order sensory areas such as the posterior parietal cortex (PPC). Thus far, there are few detailed reports investigating the single-neuron mechanisms for processing of stimulus presentation frequency in PPC. To address this gap in knowledge, we recorded PPC activity using 2-photon calcium imaging and electrophysiology during a visual oddball paradigm. Calcium imaging results reveal differentiation at the level of single neurons for frequent versus rare conditions which varied depending on whether the stimulus was preferred or non-preferred by the recorded neural population. Such differentiation of oddball conditions was mediated primarily by stimulusindependent adaptation in the frequent condition. Behavioral flexibility requires the brain to generate distinct patterns of neural responses when a stimulus is observed frequently versus rarely. For example, a wild deer that encounters a car on a daily basis may perceive rare, intermittent encounters differently. The latter case is much more surprising since the stimulus (driving car) possesses substantially different features from the usual experienced environment. Accordingly, there must be circuitry in the brain that is able to differentiate such scenarios. The oddball paradigm is a classic sensory stimulus assay used to evaluate neural differentiation of stimulus presentation frequency 1,2. In this paradigm, the neural response to a rare, deviant stimulus is compared to the response to a frequently-presented standard stimulus; differentiation of the two conditions is quantified as the difference in responses between the standard and deviant (called mismatch negativity). Specifically, the mismatch negativity (MMN) is a neurophysiological difference waveform peaking in the 150-250 ms window after stimulus onset. The MMN refers to the difference in evoked response to the standard and deviant stimulus. Importantly, the MMN is distinct from the N100 (occurring between 50 and 150 ms post stimulus onset) and the P300 (occurring around 300-400 ms) components with respect to function and timing relative to stimulus onset 3,4. The MMN has been studied comprehensively in humans using EEG, MEG, and fMRI 5-10 , and to a lesser extent, in animal models with local field potential (LFP) and/or single units 11-16. Yet, few studies have extensively probed how individual neurons exhibit responses to oddball conditions as a function of stimulus properties. Stimulus preference and tuning in single neurons may influence MMN responses, highlighting the need for neural recordings at higher spatial granularity using methods such as 2-photon calcium imaging. It has been postulated that the MMN is a precursor to sensory discrimination 17,18. Within this framework, sensory ar...