Disparity sensitivity in man and owl: Psychophysical evidence for equivalent perception of shape-from-stereo

Sensory systems in birds: What we have learned from studying sensory specialists

"Diversity" is an apt descriptor of the research career of Jack Pettigrew as it ranged from the study of trees, to clinical conditions, to sensory neuroscience. Within sensory neuroscience, he was fascinated by the evolution of sensory systems across species. Here, we review some of his work on avian sensory specialists and research that he inspired in others. We begin with an overview of the importance of the Wulst in stereopsis and the need for further study of the Wulst in relation to binocularity across avian species. Next, we summarize recent anatomical, behavioral, and physiological studies on optic flow specializations in hummingbirds. Beyond vision, we discuss the first evidence of a tactile "fovea" in birds and how this led to detailed studies of tactile specializations in waterfowl and sensorimotor systems in parrots. We then describe preliminary studies by Pettigrew of two endemic Australian species, the plains-wanderer (Pedionomus torquatus) and letter-winged kite (Elanus scriptus), that suggest the evolution of some unique auditory and visual specializations in relation to their unique behavior and ecology. Finally, we conclude by emphasizing the importance of a comparative and integrative approach to understanding avian sensory systems and provide an example of one system that has yet to be properly examined: tactile facial bristles in birds. Through reviewing this research and offering future avenues for discovery, we hope that others also embrace the comparative approach to understanding sensory system evolution in birds and other vertebrates.

Indicators and Criteria of Consciousness in Animals and Intelligent Machines: An Inside-Out Approach

In today's society, it becomes increasingly important to assess which non-human and non-verbal beings possess consciousness. This review article aims to delineate criteria for consciousness especially in animals, while also taking into account intelligent artifacts. First, we circumscribe what we mean with "consciousness" and describe key features of subjective experience: qualitative richness, situatedness, intentionality and interpretation, integration and the combination of dynamic and stabilizing properties. We argue that consciousness has a biological function, which is to present the subject with a multimodal, situational survey of the surrounding world and body, subserving complex decision-making and goal-directed behavior. This survey reflects the brain's capacity for internal modeling of external events underlying changes in sensory state. Next, we follow an inside-out approach: how can the features of conscious experience, correlating to mechanisms inside the brain, be logically coupled to externally observable ("outside") properties? Instead of proposing criteria that would each define a "hard" threshold for consciousness, we outline six indicators: (i) goal-directed behavior and model-based learning; (ii) anatomic and physiological substrates for generating integrative multimodal representations; (iii) psychometrics and meta-cognition; (iv) episodic memory; (v) susceptibility to illusions and multistable perception; and (vi) specific visuospatial behaviors. Rather than emphasizing a particular indicator as being decisive, we propose that the consistency amongst these indicators can serve to assess consciousness in particular species. The integration of scores on the various indicators yields an overall, graded criterion for consciousness, somewhat comparable to the Glasgow Coma Scale for unresponsive patients. When considering theoretically derived measures of consciousness, it is argued that their validity should not be assessed on the basis of a single quantifiable measure, but requires cross-examination across multiple pieces of evidence, including the indicators proposed here. Current intelligent machines, including deep learning neural networks (DLNNs) and agile robots, are not indicated to be conscious yet. Instead of assessing machine consciousness by a brief Turing-type of test, evidence for it may gradually accumulate when we study machines ethologically and across time, considering multiple behaviors that require flexibility, improvisation, spontaneous problem-solving and the situational conspectus typically associated with conscious experience.

[Comparative analysis of light sensitivity, depth and motion perception in animals and humans]

BACKGROUND

This study examined how humans perform regarding light sensitivity, depth perception and motion vision in comparison to various animals.

OBJECTIVE

The parameters that limit the performance of the visual system for these different functions were examined.

METHODS

This study was based on literature studies (search in PubMed) and own results.

RESULTS

Light sensitivity is limited by the brightness of the retinal image, which in turn is determined by the f‑number of the eye. Furthermore, it is limited by photon noise, thermal decay of rhodopsin, noise in the phototransduction cascade and neuronal processing. In invertebrates, impressive optical tricks have been developed to increase the number of photons reaching the photoreceptors. Furthermore, the spontaneous decay of the photopigment is lower in invertebrates at the cost of higher energy consumption. For depth perception at close range, stereopsis is the most precise but is available only to a few vertebrates. In contrast, motion parallax is used by many species including vertebrates as well as invertebrates. In a few cases accommodation is used for depth measurements or chromatic aberration. In motion vision the temporal resolution of the eye is most important. The ficker fusion frequency correlates in vertebrates with metabolic turnover and body temperature but also has very high values in insects. Apart from that the flicker fusion frequency generally declines with increasing body weight.

CONCLUSION

Compared to animals the performance of the visual system in humans is among the best regarding light sensitivity, is the best regarding depth resolution and in the middle range regarding motion resolution.

The Stereoscopic Anisotropy Develops During Childhood

Purpose

Human vision has a puzzling stereoscopic anisotropy: horizontal depth corrugations are easier to detect than vertical depth corrugations. To date, little is known about the function or the underlying mechanism responsible for this anisotropy. Here, we aim to find out whether this anisotropy is independent of age. To answer this, we compare detection thresholds for horizontal and vertical depth corrugations as a function of age.

Methods

The depth corrugations were defined solely by the horizontal disparity of random dot patterns. The disparities depicted a horizontal or vertical sinusoidal depth corrugation of spatial frequency 0.1 cyc/deg. Detection thresholds were obtained using Bayesian adaptive staircases from a total of 159 subjects aged from 3 to 73 years. For each participant we computed the anisotropy index, defined as the log₁₀-ratio of the detection threshold for vertical corrugations divided by that for horizontal.

Results

Anisotropy index was highly variable between individuals but was positive in 87% of the participants. There was a significant correlation between anisotropy index and log-age (r = 0.21, P = 0.008) mainly driven by a significant difference between children and adults. In 67 children aged 3 to 13 years, the mean anisotropy index was 0.34 ± 0.38 (mean ± SD, meaning that vertical thresholds were on average 2.2 times the horizontal ones), compared with 0.59 ± 0.55 in 84 adults aged 18 to 73 years (vertical 3.9 times horizontal). This was mainly driven by a decline in the sensitivity to vertical corrugations. Children had poorer stereoacuity than adults, but had similar sensitivity to adults for horizontal corrugations and were actually more sensitive than adults to vertical corrugations.

Conclusions

The fact that adults show stronger stereo anisotropy than children raises the possibility that visual experience plays a critical role in developing and strengthening the stereo anisotropy.

Similar mechanisms underlie the detection of horizontal and vertical disparity corrugations

Our aim was to compare sensitivity for horizontal and vertical disparity corrugations and to resolve whether these stimuli are processed by similar or radically different underlying mechanisms. We measure global disparity sensitivity as a function of carrier spatial frequency for equi-detectable carriers and found a similar optimal carrier relationship for vertical and horizontal stimuli. Sensitivity as a function of corrugation spatial frequency for stimuli of comparable spatial summation and composed of optimal, equi-detectable narrowband carriers did not significantly differ for vertical and horizontal stimuli. A small anisotropy was revealed when fixed, high contrast broadband carriers were used. In a separate discrimination-at-threshold experiment, multiple mechanisms of similar tuning were revealed to underlie the detection of both vertical and horizontal disparity corrugations. We conclude that the processing of the horizontal and vertical disparity corrugations occurs along similar lines.

Mechanisms underlying global stereopsis in fovea and periphery

To better understand the pooling properties underlying global stereopsis we examined the relationship between carrier luminance spatial frequency and modulator disparity spatial frequency. Thresholds for detecting global sinusoidal disparity corrugations of spatially band-pass noise were measured as a function of modulator disparity spatial frequency for both centrally and peripherally located stimuli using a standard 2-IFC task. We found a characteristic relationship that depended on modulator disparity spatial frequency. At high modulator disparity spatial frequencies (>1c/d), there is an optimal ratio of around 2.6, whereas at low modulator disparity spatial frequencies, there is an optimal absolute carrier luminance spatial frequency (i.e., 3c/d). In the periphery, vision is restricted to modulator disparity spatial frequencies below 1c/d and, as a consequence, following the above rule, there is an optimum absolute carrier luminance spatial frequency that reduces in spatial frequency with increasing eccentricity. This finding is consistent with there being more than one channel processing global stereo that is subsequently confirmed using a 2×2 AFC detection/discrimination paradigm. Furthermore, because of the different carrier/modulator relationships in central and peripheral vision, peripheral global stereo cannot be simply related to central global stereo by a scaling factor and thus cannot be simply due to cortical magnification, as originally thought.

Overt attention toward oriented objects in free-viewing barn owls

Visual saliency based on orientation contrast is a perceptual product attributed to the functional organization of the mammalian brain. We examined this visual phenomenon in barn owls by mounting a wireless video microcamera on the owls' heads and confronting them with visual scenes that contained one differently oriented target among similarly oriented distracters. Without being confined by any particular task, the owls looked significantly longer, more often, and earlier at the target, thus exhibiting visual search strategies so far demonstrated in similar conditions only in primates. Given the considerable differences in phylogeny and the structure of visual pathways between owls and humans, these findings suggest that orientation saliency has computational optimality in a wide variety of ecological contexts, and thus constitutes a universal building block for efficient visual information processing in general.