Familiarity-Based Object Recognition across Animacy and Real-World Size

Previous evidence suggests that parahippocampal cortex (PhC) is associated with contextual encoding and retrieval while perirhinal cortex (PrC) is associated with item familiarity. However, this is inconsistent with recent evidence that PhC is associated with item familiarity for some objects (Martin et al., 2013). The familiarity of items seems to be represented in both PhC and PrC, with object categories being represented in one area more strongly than the other, or dually associated in both. Stimuli properties of items in these categories are thought to play a role in this differential association. The purpose of the current experiment is to create an effective experimental paradigm that will be used in a future imaging study to examine the representation of item-based familiarity signals in PhC and PrC, as a function of varying stimulus dimensions. Thirty-nine students were recruited through the Psychology Research Participation Pool and were compensated 1.5 research credits for their participation. A continuous recognition memory task was employed, where items from three stimulus categories, animals, tools, and appliances, were presented and recognition memory responses were recorded. Through data analysis and iterative refinement of the paradigm, it was found that the fourth version of the paradigm should be used for a future imaging study because responses are primarily familiarity-based, overall recognition is significantly greater than chance, and two of the three stimulus categories are matched in performance. Familiarity-Based Object Recognition 3 Familiarity-Based Object Recognition across Animacy and Real-World Size Mapping out regions of the brain associated with cognitive processes and memory is an important part of neuroscientific research and one that is being studied more frequently. Memory is a complex process and although there have been numerous experiments studying the neural correlates of memory in the extant literature, there are many aspects of memory that still need to be explored. One particular memory process that has received much attention in the cognitive, neuropsychological, and neuroimaging literature is recognition memory. Recognition Memory: Recollection and Familiarity Recognition memory is the ability to recognize stimuli that have been previously encountered (Eichenbaum, Yonelinas, & Ranganath, 2007). People encounter countless stimuli every day and some of these stimuli may be more memorable than others, such that they are easier to recognize when they are reencountered. This may be differentiated into two types of recognition memory: recollection and familiarity. Recollection is described as the retrieval of contextual details when the stimulus is reencountered, while familiarity is described as a feeling of knowing of the reencountered stimulus, without any additional contextual information retrieved (Eichenbaum et al., 2007). For example, if an individual recognizes someone walking down the street because they work with that person, it would be recollection because they are retrieving contextual details about the building they work in, the job, and any number of details they have associated with that person. If the same individual recognized someone walking down the street, but did not recall from where they knew them or any contextual details about them, but they felt like they knew that person, it would be familiarity. Recognition memory has been studied in the extant literature from a neuroscientific approach and the areas of the brain correlated with recognition memory have been identified. Familiarity-Based Object Recognition 4 In a review of studies addressing the neural correlates of declarative memory, Manns and Eichenbaum (2006) proposed a highly influential view that recognition memory is supported by the medial temporal lobes; specifically, the hippocampus and parahippocampal region, which is a region that can be subdivided into parahippocampal, perirhinal and entorhinal cortex. Similar to the two types of recognition memory, it was proposed that the medial temporal lobes are functionally divided into cortex associated with recollection or familiarity. The hippocampus and parahippocampal cortex (PhC) are associated with recollection, while perirhinal cortex (PrC) is associated with familiarity (Manns and Eichenbaum, 2006). Although these regions are each associated with a single type of recognition memory, like many regions of the brain, there is an interplay between the different areas of the medial temporal lobe, characterizing a highly interconnected neural network. Binding of Item and Context Model Ranganath (2010) proposed that episodic memory is processed within the medial temporal lobes. Episodic memory is memory associated with a person’s life and their past experiences (Eichenbaum et al., 2007). Recognition memory is a type of episodic memory because recognition requires that one must have personally encountered the stimulus. Ranganath (2010) proposed a network of neural connections in the medial temporal lobes, called the Binding of Item and Context (BIC) model. In agreement with previous literature, Ranganath (2010) proposed that PhC was solely associated with the encoding and retrieval of contextual representations and that PrC was solely associated with the familiarity of items. The BIC model suggests that the contextual representations of a stimulus can strongly impact item representation, so PhC can thus have a strong effect on PrC. The BIC model also suggests that contextual information and the item representations converge in the hippocampus, where they Familiarity-Based Object Recognition 5 are “bound” together. This lends support to recollection memory, where the contextual details are retrieved with the reencountered item because the memories of the two are intertwined. Conversely, brain signal activation during familiarity responses are proposed to be localized to PrC. The BIC model suggests that context and item representations remain separate in the medial temporal lobes until they reach the hippocampus. However, the BIC model and the sectioning of PhC and PrC into different functional regions does not always hold amongst all stimuli used in recognition memory tasks. Familiarity in Medial Temporal Lobes In a recent experiment, item-based familiarity was examined in the activation of PhC and PrC, across three different categories of stimuli (Martin, McLean, O’Neil, & Kohler, 2013). Martin et al. (2013) found that activation in the PhC is associated with some categories of objects; these categories show a correlation with familiarity signals in PhC. PhC was also more active than PrC, suggesting a preferential activation for some categories of stimuli. This suggests a difference in item-based familiarity signals across stimulus categories, where some stimulus categories are represented in PhC, but other categories are represented in PrC. Martin et al. (2013) investigated how item categories are represented in brain regions during familiarity responses and sought to determine which characteristics of these stimuli categories mediate familiarity signals between PhC and PrC. This question was motivated by an imaging study by Martin et al. (2013) which examined if the PhC, which is anatomically adjacent to PrC, supports item-based familiarity signals. Familiarity was examined across three categories of stimuli: faces, chairs and buildings. The experimental task started with an encoding stage, where face, chair, and building images were presented to the participant, who was asked to make an attractive, comfort or value Familiarity-Based Object Recognition 6 judgement, respectively. The encoding stage was completed prior to scanning, and approximately an hour after the encoding stage, the participants entered the fMRI scanner to perform the testing stage. In the scanner, they were presented with stimuli of faces, chairs and buildings. They were asked to make a judgement after the presentation of the stimulus, on a familiarity scale, where one was ‘not familiar’ and four was ‘very familiar’. There was also a fifth response of ‘recollection’, if the participant happened to retrieve contextual details during the recognition response. Some of the stimuli presented were “old” and had been presented once in the encoding stage, while some stimuli were novel. This experiment focused on familiarity so the design intentionally minimized contextual details in the items. Specifically, the stimuli had all background contextual details removed and item analyses were completed in a pilot study to ensure that the items supported familiarity responses. The participants were instructed to make a fast judgement on the presented item and to attempt to avoid intentional recollection of details, to decrease the frequency of recollection responses. The results of Martin et al. (2013) demonstrates that the precautions taken to avoid recollection responses were effective because the frequency of familiarity responses was greater than that of recollection responses. There were four regions of interest (ROI) that were studied in the fMRI analyses: PhC, PrC, anterior hippocampus and posterior hippocampus. Between the three item categories, the anterior and posterior hippocampus did not show a significant change in activation. Chairs elicited significant activation in PhC, as well as PrC. Buildings elicited significant activation in PhC, while faces elicited significant activation in PrC. In summary, chairs were associated with both PhC and PrC, buildings were only associated with PhC and faces were only associated with PrC, in terms of item-based familiarity signals. Familiarity-Based Object Recognition 7 These findings are contrary to the BIC model, which proposed that PhC is solely associated with contextual information while PrC is solely associated with item familiarity. These results suggest that the BIC model is too exclusive by defining a rigid differentiation bet