Visual perception

Vision is a critical sense for many species, with the perception of motion being a fundamental aspect. This aspect often provides richer information than static images for understanding the environment. Motion recognition is a relatively simple computation compared to shape recognition. Many creatures can discriminate moving objects quite well while having virtually no capacity for recognizing stationary objects.
Traditional methods for collision-free navigation require the reconstruction of a 3D model of the environment before planning an action. These methods face numerous limitations as they are computationally expensive and struggle to scale in unstructured and dynamic environments with a multitude of moving objects.
This thesis proposes a more scalable and efficient alternative approach without 3D reconstruction. We focus on visual motion cues, specifically ’visual looming’, the relative expansion of objects on an image sensor. This concept allows for the perception of collision threats and facilitates collision-free navigation in any environment, structured or unstructured, regardless of the vehicle’s movement or the number of moving objects present.

Visual working memory (VWM) is a core cognitive system that supports our ability to maintain and manipulate visual information temporarily when sensory information is no longer present in the environment. VWM and mental rotation, a form of mental imagery, require the ability to generate internal images in the absence of stimuli. Both cognitive processes share visual buffer and are associated with representing and manipulating visual information, however, little is known about the intersection between VWM and mental rotation. In the current work, mental rotation was adopted to study updated mnemonic contents in VWM. In this dissertation, I asked whether the brain mechanisms that support VWM and mental rotation overlap. Participants were asked to remember the orientation of grating or to remember and manipulate, that is mentally rotate, the orientation of grating. Behavioral results showed that mental rotation induced lower fidelity representations of orientation. This confirmed that additional usage in visual buffer to manipulate the visual representation provoked by mental rotation involved negative influence in memory fidelity. In the second study, EEG recording was conducted while participants performed the same task. Visual representations were reconstructed from brain oscillations using the inverted encoding model (IEM). It was found that orientation information from the reconstruction was represented in the amplitude of alpha oscillations (8 – 12 Hz) for both maintained and updated mnemonic contents. Together, this work provides evidence that memory manipulation driven by mental rotation has a decisive effect on the fidelity of visual representations in VWM. Additionally this dissertation demonstrates that the updated memory representations as well as the maintained memory representations are carried in EEG oscillations.

Interocular grouping during binocular rivalry occurs when two images concurrently presented to two eyes are combined as a coherent pattern as if perceptual experience follows Gestalt grouping principles. The present study investigated what determines rivalry dynamics (perceptual experience of monocular stimuli and interocular grouping) by examining individual differences. Specifically, the effect of eye-of-origin and pattern coherence on percepts during rivalry were individually assessed using pairs of stimuli that induce either monocularly-driven (monocular coherence condition) or interocularly-driven (interocular coherence condition) coherent percepts. We found that the degree of perceiving complete, coherent stimuli was consistent within individuals regardless of conditions, indicating that individual differences in experiencing interocular grouping were explained by pattern coherence, rather than eye-of-origin information. In addition, we found that individuals who experience binocularly presented pattern motion more perceived interocularly-coherent stimuli more. This result suggests that a potential common mechanism may mediate binocular integration of visual information during binocular rivalry.

Spatial-based attention is shown to vary in strength over short intervals of time. Whether object-based selection also has similar temporal variability is not known. Egly, Driver and Rafal (1994) demonstrated using 2-rectangle displays how both spatial and object-based selection engages in processing of a visual scene. In Experiment-1 using the 2-rectangle paradigm we measured temporal variability of target detection by presenting targets at a variable SOA. In Experiment-2, we used 4-squares to preclude any object-based selection and measured temporal variability in target detection at similar locations as in Experiment-1. We found target detection to be periodic in delta and theta hertz rhythm in both Experiment-1 and Experiment-2 upon comparing corresponding cue-valid and same-object locations. Similar spectral profiles across experiments indicate a split-spotlight of spatial attention that rhythmically monitors cue-valid and other invalid locations. Future experiments are needed to determine whether object-based selection is periodic in nature.

Working memory (WM) is an important cognitive function that, among other duties, allows temporary storage of visual representations of objects observed in the sensorium. The visual aspect of this core cognitive function enables our perception of the identity of objects and where those objects are located in space at any particular time to help direct attention. In a typical working memory task, a cue is presented beforehand to guide attention to which objects in an array to encode. The performance of our WM abilities can be improved on memory tasks by a retrospective cue resented after the encoding process of working memory. Several mechanisms have been proposed to explain etrospective cue benefits in WM performance, including the removal of irrelevant information from WM, attentional enhancement of the cued representation, protection of the cued representation from subsequent decay or interference, or retrieval head start.

A thorough delineation of the extent of processing possible without visual awareness is necessary to elucidate the neural mechanisms of visual awareness. Despite extensive research, it is presently unclear whether invisible stimuli can undergo advanced processing. To introduce existing work on this topic, previous behavioral efforts to investigate the extent of processing possible without visual awareness and the psychophysical methods used to render stimuli invisible, such as visual masking and interocular suppression-based techniques, are discussed. Physiological evidence that provide support for and against the possibility that advanced information processing can occur without visual awareness are addressed. The basics of multivariate pattern classification techniques are outlined. The potential of using multivariate pattern classification analyses in conjunction with neuroimaging in the temporal domain to investigate whether advanced processing can occur without visual awareness is discussed. An original study using electroencephalography (EEG) and pattern classification techniques to investigate the extent of processing possible without visual awareness is outlined. The results of the analyses reveal that a pattern classifier did not extract neural signatures of categorical processing from EEG recordings when participants viewed an image that remained invisible for the duration of its presentation. In contrast, the results from a second experiment reveal that the pattern classifier was able to decode the category of invisible images from the EEG time series when the images would eventually become visible. The results provide support for the idea that under certain circumstances, such as when the depth of interocular suppression is reduced, advanced processing for invisible stimuli can occur.

The current study sought to examine further the concept of
eyewitness memory for events. Specifically, using filmed events that were
performed with objects and events performed without objects, we explored
the potential interaction of the object cue and binding or conjunction
errors. This specific memory error involves improperly pairing two or more
feature memories together in the long-term store. In our study, these
features were the action and the actress performing the action. Our study
involved 51 participants. Participants were shown target events in Week 1
and asked to retrieve the target events from a larger group of events in
Week 2. While findings did not show the expected interaction of
conjunction events to object presence or absence, objects without an
object showed a significantly higher acceptance rate. A secondary analysis revealed an interaction effect between head-focus and
recognition item type, meaning participants did view events without an
object differently from objects with an object.

In the present study, it was examined whether the spatiotemporal dynamics of
transitions towards target dominance in motion-induced blindness (MIB) were wave-like,
similar to those in binocular rivalry. The spatiotemporal dynamics of transitions towards
dominance in MIB were further compared with those in binocular rivalry to reveal a
potential neural locus of MIB. Across a series of experiments, the relationship between
target length, stimulus structure, presentation location and the latency for circular arc
segment-shaped targets to reappear was examined, respectively. It was found that target
reappearance durations increase with target length, as if they reappear in a gradual, wavelike
fashion. Target reappearance durations were decreased for collinear compared to
radial targets, but they were not influenced by the location of target presentation. The
results suggest MIB target reappearances are associated with traveling waves of
dominance, and early visual cortex is a likely neural substrate in which these wave-like
transitions occur.

Eye fixations of the face are normally directed towards either the eyes or the
mouth, however the proportions of gaze to either of these regions are dependent on
context. Previous studies of gaze behavior demonstrate a tendency to stare into a target’s
eyes, however no studies investigate the differences between when participants believe
they are engaging in a live interaction compared to knowingly watching a pre-recorded
video, a distinction that may contribute to studies of memory encoding. This study
examined differences in fixation behavior for when participants falsely believed they
were engaging in a real-time interaction over the internet (“Real-time stimulus”)
compared to when they knew they were watching a pre-recorded video (“Pre-recorded
stimulus”). Results indicated that participants fixated significantly longer towards the
eyes for the pre-recorded stimulus than for the real-time stimulus, suggesting that
previous studies which utilize pre-recorded videos may lack ecological validity.

Most of the human visual field falls in the periphery, and peripheral processing is
important for normal visual functioning. Yet, little is known about peripheral object
recognition in naturalistic scenes and factors that modulate this ability. We propose that
a critical function of scene and object memory is in order to facilitate visual object
recognition in the periphery. In the first experiment, participants identified objects in
scenes across different levels of familiarity and contextual information within the scene.
We found that familiarity with a scene resulted in a significant increase in the distance
that objects were recognized. Furthermore, we found that a semantically consistent scene
improved the distance that object recognition is possible, supporting the notion that
contextual facilitation is possible in the periphery. In the second experiment, the preview
duration of a scene was varied in order to examine how a scene representation is built and
how memory of that scene and the objects within it contributes to object recognition in
the periphery. We found that the closer participants fixated to the object in the preview,
the farther on average they recognized that target object in the periphery. However, only a preview duration of the scenes for 5000 ms produced significantly farther peripheral
object recognition compared to not previewing the scene. Overall, these experiments
introduce a novel research paradigm for object recognition in naturalistic scenes, and
demonstrates multiple factors that have systematic effects on peripheral object
recognition.