Biomedical subjects

Joel Pearson

Publications and source records attributed to Joel Pearson.

9 recordsLinked to original sources

PubMed2005

Suppressed patterns alter vision during binocular rivalry.

Binocular rivalry occurs when incongruent patterns are presented to corresponding regions of the retinas, leading to fluctuations of awareness between the patterns . One attribute of a stimulus may rival whereas another may combine between the eyes , but it is typically assumed that the dominant features are perceived veridically. Here, we show this is not necessarily the case and that a suppressed visual feature can alter dominant perception. The cortical representations of oriented gratings can interact even when one of them is perceptually suppressed, such that the perceived orientation of the dominant grating is systematically biased depending on the orientation of the suppressed grating. A suppressed inducing pattern has the same qualitative effect as a visible one, but suppression reduces effective contrast by a factor of around six. A simple neural model quantifies and helps explain these illusions. These results demonstrate that binocular rivalry suppression operates in a graded fashion across multiple sites in the visual hierarchy rather than truncating processing at a single site and that suppressed visual information can alter dominant vision in real-time.

Humans↗

PubMed2005

Mechanisms selectively engaged in rivalry: normal vision habituates, rivalrous vision primes.

When rivalrous stimuli are presented intermittently, perception stabilises. This indicates the operation of perceptual memory across interruptions in stimulation. Here we show that a percept under non-rivalrous and rivalrous conditions has qualitatively different effects on subsequent rivalrous vision. When an image is perceived under rivalrous viewing, that image is more likely to be perceived in later rivalrous viewing: an effect of stabilisation or priming. When the same image is perceived under non-rivalrous viewing conditions, it is less likely to be perceived again during subsequent rivalrous viewing: an effect of adaptation or habituation. When these stimuli possess different attributes to those in subsequent vision their effect declines. This suggests that visual rivalry might recruit mechanisms that are not engaged in 'normal' non-rivalrous vision but perhaps dedicated to the resolution of competing sensory information.

Awareness↗

PubMed2005

When your brain decides what you see: grouping across monocular, binocular, and stimulus rivalry.

Research suggests that the neural concomitants of visual rivalry are contingent on the stimulus parameters, implying the existence of three different types of rivalry. Binocular rivalry (dissimilar patterns are presented, one to each eye) is seemingly mediated by interactions between pools of monocular neurons. Monocular rivalry (superimposed patterns are presented to one or both eyes) is presumably the result of competition between neural representations of the patterns. Stimulus rivalry (dissimilar patterns are swapped rapidly between the two eyes) is independent of eye of origin. In the experiment reported here, we integrated these three different types of rivalry into one stimulus. We found that perceptual alternations span the three types of rivalry, demonstrating that the brain can produce a coherent percept sourced from three different types of visual conflict. This result is in agreement with recent work suggesting that the resolution of competitive visual stimuli is mediated by a general mechanism spanning different levels of the visual-processing hierarchy.

Brain↗

PubMed2004

Rapid global form binding with loss of associated colors.

Distributed neural processing creates a binding problem: the representations of the various features of an object are distributed across brain areas but must be associated with, or bound to, the same object. Here we determine the limits that binding imposes on the perception of global form in static flow fields defined by oriented dot pairs. The binding of local orientation signals into global form is shown to operate at rapid 20-Hz rates, implying that visual signals at the point of global form extraction retain precise temporal registration. Binding global form with color is limited to rates of 3-5Hz, showing that binding across attributes can impose a severe temporal limit on perception. Judgment of the temporal sequence of the global structures is also limited to slow rates. These results point to a substantial loss of temporal resolution in the visual system following the extraction of global form but preceding visual awareness.

Awareness↗

PubMed2004

Perceptual grouping of biological motion promotes binocular rivalry.

Investigation of perceptual rivalry between conflicting stimuli presented one to each eye can further understanding of the neural underpinnings of conscious visual perception. During rivalry, visual awareness fluctuates between perceptions of the two stimuli. Here, we demonstrate that high-level perceptual grouping can promote rivalry between stimulus pairs that would otherwise be perceived as nonrivalrous. Perceptual grouping was generated with point-light walker stimuli that simulate human motion, visible only as lights placed on the joints. Although such walking figures are unrecognizable when stationary, recognition judgments as complex as gender and identity can accurately be made from animated displays, demonstrating the efficiency with which our visual system can group dynamic local signals into a globally coherent walking figure. We find that point-light walker stimuli presented one to each eye and in different colors and configurations results in strong rivalry. However, rivalry is minimal when the two walkers are split between the eyes or both presented to one eye. This pattern of results suggests that processing animated walker figures promotes rivalry between signals from the two eyes rather than between higher-level representations of the walkers. This leads us to hypothesize that awareness during binocular rivalry involves the integrated activity of high-level perceptual mechanisms in conjunction with lower-level ocular suppression modulated via cortical feedback.

Dominance, Ocular↗

PubMed2004

Determinants of visual awareness following interruptions during rivalry.

The inability of the human visual system to fuse dissimilar patterns in corresponding regions of the two eyes results in stochastic alternation of perceptual dominance between the two patterns: rivalry. When rivalrous stimuli are presented intermittently their perception is stabilized (Leopold, Wilke, Maier, & Logothetis, 2002). This stability indicates the operation of some kind of perceptual memory across interruptions in stimulation. Here we examined the contents of this perceptual memory to quantify the relative contributions of different sources of information: eye-of-origin, orientation, and color. Stimuli were intermittently presented and, during each blank interruption, we swapped either the color, orientation, or eye of presentation of the gratings. Comparing the percepts reported before and after each interruption allowed us to establish what aspects of perception remained stable. During conventional binocular rivalry, the eye in which the stimulus was presented remained stable across 74% of interruptions. Stimulus color and orientation also had weaker significant effects. When eye-of-origin information was eliminated by alternating the patterns rapidly between the two eyes, stimulus color remained stable across 86% of interruptions. Stimulus orientation again had a weaker but significant effect. These results demonstrate that the mechanisms mediating perceptual stability across interruptions in rivalry can operate at both monocular and binocular levels, much like the mechanisms operating during continuous viewing of rivalrous stimuli. On the basis of this similarity, we speculate that perceptual memory across interruptions in rivalry may involve the same neural representations as visual competition during rivalry. If this is the case, the use of intermittent stimulation in rivalry might permit the investigation of aspects of the mechanisms underlying visual competition that remain hidden during continuous presentation.

Awareness↗

PubMed2004

Motion transparency promotes synchronous perceptual binding.

While identified regions of human extrastriate visual cortex are functionally specialized for processing different attributes of an object, the cognitive and neural mechanisms by which these attributes are dynamically bound into integrated percepts are still largely mysterious. Here, we report that perceptual organization influences the dynamics of binding. Specifically, the perception of motion transparency promotes the synchronous perceptual binding of colour and motion, which otherwise exhibits considerable asynchronies. In addition, we demonstrate that perceptual asynchrony can be reinstated by manipulating stereoscopic disparity or speed within the stimulus. Our findings suggest that the phenomenology of colour-motion binding parallels the known physiology of motion processing in area MT of primate visual cortex, supporting the view that the dynamics of perceptual binding is a direct reflection of the time course of the underlying neural processing.

Color Perception↗

PubMed2003

Colour and luminance selectivity of spatial and temporal interactions in orientation perception.

Previous studies have commented upon the similar phenomenology of simultaneous and successive interactions in the perception of orientation. These similarities have been taken as evidence of common mechanisms underlying the simultaneous tilt illusion (TI) and the successive tilt aftereffect (TAE). We measured the TI and TAE for four subjects for combinations of test and inducing stimuli modulated along either the same or orthogonal axes of colour space within the L+M+S, L-M colour-luminance plane. The largest TI and TAE were found when test and inducer were modulated along the same axis of colour space. The TI consistently showed greater selectivity for colour/luminance than the TAE. The results are discussed in relation to the known chromatic properties of the primate visual pathways. Specifically, we suggest that both the TI and TAE involve colour- and luminance-specific neurons in primary visual cortex as well as cue-invariant mechanisms in extrastriate cortex.

Color Perception↗

PubMed2003

A paradox of temporal perception revealed by a stimulus oscillating in colour and orientation.

Psychophysical experiments with stimuli oscillating concurrently in colour and orientation revealed an apparently paradoxical dissociation between the perceived simultaneity of stimulus changes and the perceptual pairing of the events demarked by those changes. When subjects were required to report whether changes in colour and orientation were simultaneous, judgements were generally accurate within +/-10 ms. When subjects were required to report which colour was paired predominantly with which orientation, judgements showed a systematic temporal bias of up to 50 ms in favour of colour. This dissociation between different temporal judgements concerning the same stimulus sequence is not predicted by any of the current models of binding in conscious vision. We propose an account of these data based on the temporal response properties of colour- and orientation-selective model neurons such that the perceived pairing of visual attributes is modelled as the cross-correlation of time-varying neural response profiles and thus reflects both neuronal latencies and the rate of rapid adaptation rather than simply the temporal pattern of responses to stimulus transitions.

Color↗