163 research outputs found
A Common Cortical Circuit Mechanism for Perceptual Categorical Discrimination and Veridical Judgment
Perception involves two types of decisions about the sensory world:
identification of stimulus features as analog quantities, or discrimination of
the same stimulus features among a set of discrete alternatives. Veridical
judgment and categorical discrimination have traditionally been conceptualized
as two distinct computational problems. Here, we found that these two types of
decision making can be subserved by a shared cortical circuit mechanism. We used
a continuous recurrent network model to simulate two monkey experiments in which
subjects were required to make either a two-alternative forced choice or a
veridical judgment about the direction of random-dot motion. The model network
is endowed with a continuum of bell-shaped population activity patterns, each
representing a possible motion direction. Slow recurrent excitation underlies
accumulation of sensory evidence, and its interplay with strong recurrent
inhibition leads to decision behaviors. The model reproduced the
monkey's performance as well as single-neuron activity in the
categorical discrimination task. Furthermore, we examined how direction
identification is determined by a combination of sensory stimulation and
microstimulation. Using a population-vector measure, we found that direction
judgments instantiate winner-take-all (with the population vector coinciding
with either the coherent motion direction or the electrically elicited motion
direction) when two stimuli are far apart, or vector averaging (with the
population vector falling between the two directions) when two stimuli are close
to each other. Interestingly, for a broad range of intermediate angular
distances between the two stimuli, the network displays a mixed strategy in the
sense that direction estimates are stochastically produced by winner-take-all on
some trials and by vector averaging on the other trials, a model prediction that
is experimentally testable. This work thus lends support to a common
neurodynamic framework for both veridical judgment and categorical
discrimination in perceptual decision making
The puzzle of perceptual precision
This paper argues for a failure of correspondence between perceptual representation and what it is like to perceive. If what it is like to perceive is grounded in perceptual representation, then, using considerations of veridical representation, we can show that inattentive peripheral perception is less representationally precise than attentive foveal perception. However, there is empirical evidence to the contrary. The conclusion is that perceptual representation cannot ground what it is like to perceive
Change blindness: eradication of gestalt strategies
Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task
Dynamic excitatory and inhibitory gain modulation can produce flexible, robust and optimal decision-making
<div><p>Behavioural and neurophysiological studies in primates have increasingly shown the involvement of urgency signals during the temporal integration of sensory evidence in perceptual decision-making. Neuronal correlates of such signals have been found in the parietal cortex, and in separate studies, demonstrated attention-induced gain modulation of both excitatory and inhibitory neurons. Although previous computational models of decision-making have incorporated gain modulation, their abstract forms do not permit an understanding of the contribution of inhibitory gain modulation. Thus, the effects of co-modulating both excitatory and inhibitory neuronal gains on decision-making dynamics and behavioural performance remain unclear. In this work, we incorporate time-dependent co-modulation of the gains of both excitatory and inhibitory neurons into our previous biologically based decision circuit model. We base our computational study in the context of two classic motion-discrimination tasks performed in animals. Our model shows that by simultaneously increasing the gains of both excitatory and inhibitory neurons, a variety of the observed dynamic neuronal firing activities can be replicated. In particular, the model can exhibit winner-take-all decision-making behaviour with higher firing rates and within a significantly more robust model parameter range. It also exhibits short-tailed reaction time distributions even when operating near a dynamical bifurcation point. The model further shows that neuronal gain modulation can compensate for weaker recurrent excitation in a decision neural circuit, and support decision formation and storage. Higher neuronal gain is also suggested in the more cognitively demanding reaction time than in the fixed delay version of the task. Using the exact temporal delays from the animal experiments, fast recruitment of gain co-modulation is shown to maximize reward rate, with a timescale that is surprisingly near the experimentally fitted value. Our work provides insights into the simultaneous and rapid modulation of excitatory and inhibitory neuronal gains, which enables flexible, robust, and optimal decision-making.</p></div
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A psychophysical investigation of audio-visual timing in the millisecond range.
The experiments described in this thesis use psychophysical techniques and human observers to investigate temporal processing in the millisecond range. The thesis contains five main sections. Introductory chapters provide a brief overview of the visual and auditory systems, before detailing our current understanding of duration processing. During the course of this review, several important questions are highlighted. The experiments detailed in Chapters 8-11 seek to address these questions using the psychophysical techniques outlined in Chapter 7. The results of these experiments increase our understanding of duration perception in several areas. Firstly, Experiments 1 and 2 (Chapter 8) highlight the role of low level stimulus features: even when equated for visibility stimuli of differing spatial frequency have different perceived durations. Secondly, a psychophysical hypothesis arising from the ¿duration channels¿ or ¿labelled lines¿ model of duration perception is given strong support by the adaptation experiments detailed in Chapter 9 and 10. Specifically, adaptation to durations of a fixed temporal extent induces repulsive duration aftereffects that are sensory specific and bandwidth limited around the adapted duration. Finally Chapter 11 describes the results of experiments designed to probe the processing hierarchy within duration perception by measuring the interdependency of illusions generated via duration adaptation and via multisensory cue combination. The results of these experiments demonstrate that duration adaptation is a relatively early component of temporal processing and is likely to be sub served by duration selective neurons situated in early sections of the visual and auditory systems
Olfactory consciousness across disciplines
Our sense of smell pervasively influences our most common behaviors and daily experience, yet little is known about olfactory consciousness. Over the past decade and a half research in both the fields of Consciousness Studies and Olfaction has blossomed, however, olfactory consciousness has received little to no attention. The olfactory systems unique anatomy, functional organization, sensory processes, and perceptual experiences offers a fecund area for exploring all aspects of consciousness, as well as a external perspective for re-examining the assumptions of contemporary theories of consciousness. It has even been suggested that the olfactory system may represent the minimal neuroanatomy that is required for conscious processing.
Given the variegated nature of research on consciousness, we include original papers concerning the nature of olfactory consciousness. The scope of the special edition widely incorporates olfaction as it relates to Consciousness, Awareness, Attention, Phenomenal- or Access-Consciousness, and Qualia. Research concerning olfaction and cross-modal integration as it relates to conscious experience is also address.
As the initial foray into this uncharted area of research, we include contributions from across all disciplines contributing to cognitive neuroscience, including neurobiology, neurology, psychology, philosophy, linguistics, and computer sciences. It is our hope that this Research Topic will serve as the impetus for future interdisciplinary research on olfaction and consciousness
STUDY OF STABLE MOTION PERCEPTION
The goal of my PhD project was to combine approaches from human psychophysics, Bayesian modeling and animal electrophysiology to study the mechanisms underlying motion perception. The specific goals of the current project are to: i) investigate the relationship between perceptual bias and stabilization with contextual regularity and density in human observers, and develop novel Bayesian models of motion perception that can account for the data; ii) explore motion duration dependence of offset neural activity and its layer specificity in primary visual cortex (V1) of alert monkeys
The temporal context of face perception: behavioural, electrophysiological and neuroimaging correlates
Adaptation-related aftereffects (AEs) and repetition priming (PR) are two phenomena when recent experiences alter face perception. Although the behavioural reflections of AEs and PR are quite different, both phenomena share some similarities regarding their functional properties and neural correlates. As most of the previous studies focused on either one or the other phenomenon, little is known about the relationship between AEs and PR. The present studies attempted to fill this gap. Study I investigated face identity AEs and PR within the same stimulus repetition paradigm, keeping timing and task constant. Following face or Fourier phase randomized (noise) stimuli, participants classified test faces varying on a morph continuum between two famous identities. Study I showed that AEs and PR can be observed within the same paradigm and subjects, behaviourally and in event-related potentials (ERPs). Interestingly, we found identity-specific as well as category-specific ERP modulations. Study II further investigated the factors underlying face identity AEs in a similar paradigm. The results confirmed and extended the findings of Study I, e.g., there were again different ERP modulations by stimulus category and face identity. In Study III, AEs and image-specific PR were investigated in the perception of face gender using functional magnetic resonance imaging (fMRI). Study III suggested dissociations between 1) gender-specific AEs and image-specific PR in behaviour, 2) brain areas associated with AEs and PR, and 3) brain areas associated with gender-specific and categorical processes. In conclusion, the present studies showed that similarity between adaptor and test faces and ambiguity of the test face both determine whether AE or PR is observed, and suggested that exclusive mechanisms might underlie both phenomena. Our results also revealed that the processing of face identity or gender runs in parallel to object-category processing during the earlier processing stages
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