The Shadows Are Not All the Same: The Nature of Object Representations Depends on the Neural Circuits Involved
Open AccessAn object representation is the pattern of neuronal activity which is evoked by the perception of an object. The work presented in this dissertation makes the argument that object representations differ depending on the neural circuitry which is recruited in their processing, resulting in perceptual and attentional differences between objects which differ across semantic categories such as size or manipulability.In the first paper presented, we hypothesized that the real-world size of an object is encoded into the neural representation of the object, predicting that (1) the encoding of size into objects’ representation affects the perception of the objects and (2) any behavioral effects elicited by the presentation size of a stimulus are also elicited by the semantic size of objects. Experiment One used a discrimination task in which targets could appear in squares of five different sizes. Responses to targets within larger boxes were slowed compared to targets within smaller boxes, demonstrating a behavioral effect of stimulus presentation size. Experiment Two used an identical task except the squares were replaced by line images of semantic objects from two groups: small objects and large objects. It was found that the responses to targets appearing within the larger objects were slowed compared to targets appearing in the smaller objects, supporting our first prediction that perception of semantic objects is affected by the semantic size of the objects. The two experiments support our second prediction that behavioral effects elicited by the presentation size of stimuli are also elicited by semantic size, supporting our hypothesis that the real-world size of objects is encoded into the neural representation of the objects.In the second paper presented, we hypothesized that because the dorsal and ventral visual pathways have differing proportions of magno- and parvo-cellular input, there should be behavioral differences in perceptual tasks between manipulable and non-manipulable objects. This hypothesis was tested in adults across five experiments using a gap detection task, suited to the spatial resolution of parvocellular processing, and an object flicker discrimination task, suited to the temporal resolution of magnocellular processing. Directly predicted from the cellular composition of each pathway, a strong non-manipulable object advantage was observed in gap detection, and a small manipulable object advantage in flicker discrimination. Additionally, these effects are modulated by reducing object recognition through inversion and by suppressing magnocellular processing using red light. These results establish perceptual differences between objects dependent on semantic knowledge. The third paper presented is a perspective piece which discusses a set of attentional phenomena that are not easily accommodated within current theories of attentional selection. We call these phenomena attentional platypuses, as they allude to an observation that within biological taxonomies the platypus does not fit into either mammal or bird categories. Similarly, attentional phenomena that do not fit neatly within current attentional models suggest that current models are in need of a revision. We list a few instances of the “attentional platypuses” and then offer a new approach, that we term dynamically weighted prioritization, stipulating that multiple factors impinge onto the attentional priority map, each with a corresponding weight. The interaction between factors and their corresponding weights determines the current state of the priority map which subsequently constrains/guides attentional allocation. We propose that this new approach should be considered as a supplement to existing models of attention, especially those that emphasize categorical organizations. The work presented in this dissertation argues that object representations differ dependent on their semantic content, leading to differences in how objects are both perceived and attended to. The first two papers present novel hypotheses about how the semantic categories of size and manipulability are incorporated into object representations and provide experimental evidence to support the conclusion that object representations differ across the semantic categories of size and manipulability. The third paper argues that attentional effects which derive from factors such as the semantic differences between objects challenge the current theories of attentional selection, which necessitates a new view of attention such as dynamically weighted prioritization. Taken together, what we know about an object changes our representation of the object, which alters our perception of and attention to that object.
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Dubbelde_gwu_0075A_16079.pdf | 2022-10-04 | Open Access |
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