Biology subjects

Read, J. C. A.

Publications and source records attributed to Read, J. C. A..

8 recordsLinked to original sources

bioRxiv2023

The effect of information content distributions on word recollection and familiarity

This study builds on work on language processing and information theory which suggests that informationally uniform, or smoother, sequences are easier to process than ones in which information arrives in clumps. Because episodic memory is a form of memory in which information is encoded within its surrounding context, we predicted that episodic memory in particular would be sensitive to information distribution. We used the "dual process" theory of recognition memory to separate the episodic memory component (recollection) from the non-episodic component (familiarity) of recognition memory. Though we find a weak effect in the predicted direction, this does not reach statistical significance and so the study does not support the hypothesis. The study does replicate a known effect from the literature where low frequency words are more easily recognized than high frequency ones when participants employ recollection-type memory. We suggest our results may be explained by linguistic processing being particularly adapted to processing linear sequences of information in a way that episodic memory is not. Episodic memory likely evolved to deal with unpredictable, sometimes clumped, information streams.

animal behavior and cognition↗

bioRxiv2023

Accommodation and wavelength: the effect of longitudinal chromatic aberration on the stimulus-response curve.

The longitudinal chromatic aberration (LCA) of the eye creates a chromatic blur on the retina that is an important cue for accommodation. While this mechanism can work optimally in broadband illuminants such as daylight, it is not clear how the system responds to the narrowband illuminants used by many modern displays. Here, we measured pupil and accommodative responses as well as visual acuity under narrowband LED illuminants of different peak wavelengths. Observers were able to accommodate under narrowband light and compensate for the LCA of the eye, with no difference in the variability of the steady-state accommodation response between narrowband and broadband illuminants. Intriguingly, our subjects compensated more fully for LCA at nearer distances. That is, the difference in accommodation to different wavelengths became larger when the object was placed nearer the observer, causing the slope of the accommodation response curve to become shallower for shorter wavelengths and steeper for longer ones. Within the accommodative range of observers, accommodative errors were small and visual acuity normal. When comparing between illuminants, when accommodation was accurate, visual acuity was worst for blue narrowband light. This cannot be due to the sparser spacing for S-cones, since our stimuli had equal luminance and thus activated M-cones roughly equally. It is likely because ocular LCA changes more rapidly at shorter wavelength, and so the finite spectral bandwidth of LEDs corresponds to a greater dioptric range at shorter wavelengths. This effect disappears for larger accommodative errors, due to the increased depth-of-focus of the eye.

physiology↗

bioRxiv2023

Understanding accommodative control in the clinic: modeling latency and amplitude for uncorrected refractive error, presbyopia and cycloplegia

Accommodation refers to the process of increasing the optical power of the eyes crystalline lens so as to focus on objects at different distances. Refractive error is a mismatch between the physical size of the eye and its optical power when accommodation is fully relaxed, while functional presbyopia is a decrease in the range of accommodation with age that results in the near point of accommodation lying beyond the near working distance. Both conditions mean that sharp focus may not be achievable for some distances, and observers will experience sustained defocus. A familiar example is an older person struggling to read text on their phone. Here, we identify a problem with current models of the neural control of accommodation: they predict excessive internal responses to stimuli outside the range of accommodation, leading to unrealistic adaptation effects. Specifically, after a prolonged period of viewing stimuli outside their accommodative range, current models predict that observers would show long latencies in the accommodative response to stimuli within range. These latencies are not observed empirically, indicating a problem with current models. We propose a simple solution, exploiting the predictive nature of accommodative control, and demonstrate that the new model performs correctly. We also model cycloplegia as a change in gain, and include a lower bound on the neural signal driving accommodation so as to model the additional relaxation of accommodation often seen with cycloplegia. We show that with these modifications, we can obtain plausible predictions for the accommodative response and accommodative convergence signal in a wide range of clinically relevant situations such as functional presbyopia, fogging lenses, corrected and uncorrected refractive error, and cycloplegia.

neuroscience↗

bioRxiv2021

Seeing the future: predictive control in neural models of ocular accommodation

Ocular accommodation is the process of adjusting the eyes crystalline lens so as to bring the retinal image into sharp focus. The major stimulus to accommodation is therefore retinal defocus, and in essence, the job of accommodative control is to send a signal to the ciliary muscle which will minimize the magnitude of defocus. In this paper, we first provide a tutorial introduction to control theory to aid vision scientists without this background. We then present a unified model of accommodative control that explains properties of the accommodative response for a wide range of accommodative stimuli. Following previous work, we conclude that most aspects of accommodation are well explained by dual integral control, with a "fast" or "phasic" integrator enabling response to rapid changes in demand, which hands over control to a "slow" or "tonic" integrator which maintains the response to steady demand. Control is complicated by the sensorimotor latencies within the system, which delay both information about defocus and the accommodation changes made in response, and by the sluggish response of the motor plant. These can be overcome by incorporating a Smith predictor, whereby the system predicts the delayed sensory consequences of its own motor actions. For the first time, we show that critically-damped dual integral control with a Smith predictor accounts for adaptation effects as well as for the gain and phase for sinusoidal oscillations in demand. In addition, we propose a novel proportional-control signal to account for the power spectrum of accommodative microfluctuations during steady fixation, which may be important in hunting for optimal focus, and for the nonlinear resonance observed for low-amplitude, high-frequency input. Complete Matlab/Simulink code implementing the model is provided at https://doi.org/10.25405/data.ncl.14945550.

neuroscience↗

bioRxiv2018

Motion-in-depth perception and prey capture in the praying mantis

Perceiving motion-in-depth is essential to detecting approaching or receding objects, predators and prey. This can be achieved using several cues, including binocular stereoscopic cues such as changing disparity and interocular velocity differences and monocular cues such as looming. While these have been studied in detail in humans, only looming responses have been well characterized in insects and we know nothing about the role that stereo cues play and how they might interact with looming cues. We used our 3D insect cinema in a series of experiments to investigate the role of the stereo cues mentioned above, as well as looming, in the perception of motion-in-depth during predatory strikes by the praying mantis. Our results show that motion-in-depth does increase the probability of mantis strikes but only for the classic looming stimulus, an expanding luminance edge. Approach indicated by radial motion of a texture or expansion of a motion-defined edge, or by stereoscopic cues, all failed to elicit increased striking. We conclude that mantises use stereopsis to detect depth but not motion-in-depth, which is detected via looming.\n\nSummary StatementBoth stereoscopic visual cues and changing luminance cues can enable detection of approaching objects. We show that mantises use looming rather than stereo cues to detect motion-in-depth.

animal behavior and cognition↗

bioRxiv2018

Current models cannot account for V1’s specialisation for binocular natural image statistics

A long-standing observation about primary visual cortex (V1) is that the stimulus selectivity of neurons can be well explained with a cascade of linear computations followed by a nonlinear rectification stage. This framework remains highly influential in systems neuroscience and has also inspired recent efforts in artificial intelligence. The success of these models include describing the disparity-selectivity of binocular neurons in V1. Some aspects of real neuronal disparity responses are hard to explain with simple linear-nonlinear models, notably the attenuated response of real cells to \"anticorrelated\" stimuli which violate natural binocular image statistics. General linear-nonlinear models can account for this attenuation, but no one has yet tested whether they quantitatively match the response of real neurons. Here, we exhaustively test this framework using recently developed optimisation techniques. We show that many cells are very poorly characterised by even general linear-nonlinear models. Strikingly, the models can account for neuronal responses to unnatural anticorrelated stimuli as well as to most natural, correlated stimuli. However, the models fail to capture the particularly strong response to binocularly correlated stimuli at the preferred disparity of the cell. Thus, V1 neurons perform an amplification of responses to correlated stimuli which cannot be accounted for by a linear-nonlinear cascade. The implication is that even simple stimulus selectivity in V1 requires more complex computations than previously envisaged.\n\nSignificance statementA long-standing question in sensory systems neuroscience is whether the computations performed by neurons in primary visual cortex can be described by repeated elements of linear-nonlinear units (a linear filtering/pooling stage followed by a subsequent output nonlinearity, such as a squaring). This question goes back to the Nobel-prize winning work by Hubel & Wiesel who argued that orientation selectivity in V1 can qualitatively be explained in this way. In this paper, we show that V1 neurons have an amplification of their response to stimuli which are contrast matched in the two eyes, and that the recovered models cannot describe this property. We argue that this likely represents more sophisticated computations than can be compactly described by the linear-nonlinear cascade framework.

neuroscience↗

bioRxiv2018

A stimulus artefact undermines the evidence for independent ON and OFF channels in stereopsis

Early vision proceeds through distinct ON and OFF channels, which encode luminance increments and decrements respectively. It has been argued that these channels also contribute separately to stereoscopic vision. This is based on the fact that observers perform better on a noisy disparity discrimination task when the stimulus is a random-dot pattern consisting of equal numbers of black and white dots (a \"mixed-polarity stimulus\", argued to activate both ON and OFF stereo channels), than when it consists of all-white or all-black dots (\"same-polarity\", argued to activate only one). However, it is not clear how this theory can be reconciled with our current understanding of disparity encoding. Recently, a binocular convolutional neural network was able to replicate the mixed-polarity advantage shown by human observers, even though it was based on linear filters and contained no mechanisms which would respond separately to black or white dots. Here, we show that the stimuli used in all these experiments contain a subtle artefact. The interocular correlation between left and right images is actually lower for the same-polarity stimuli than for mixed-polarity stimuli with the same amount of disparity noise applied to the dots. Since our current theories suggest stereopsis is based on a correlation-like computation in primary visual cortex, it is then unsurprising that performance was better for the mixed-polarity stimuli. We conclude that there is currently no evidence supporting separate ON and OFF channels in stereopsis.

neuroscience↗

bioRxiv2017

When invisible noise obscures the signal: the consequences of nonlinearity in motion detection

1The motion energy model is the standard account of motion detection in animals from beetles to humans. Despite this common basis, we show here that a difference in the early stages of visual processing between mammals and insects leads this model to make radically different behavioural predictions. In insects, early filtering is spatially lowpass, which makes the surprising prediction that motion detection can be impaired by \"invisible\" noise, i.e. noise at a spatial frequency that elicits no response when presented on its own as a signal. We confirm this prediction using the optomotor response of praying mantis Sphodromantis lineola. This does not occur in mammals, where spatially bandpass early filtering means that linear systems techniques, such as deriving channel sensitivity from masking functions, remain approximately valid. Counter-intuitive effects such as masking by invisible noise may occur in neural circuits wherever a nonlinearity is followed by a difference operation.

neuroscience↗