Motion perception

Motion perception is the process of inferring the speed and direction of elements in a scene based on visual, vestibular and proprioceptive inputs.

The inability to perceive motion is called akinetopsia and it may be caused by a lesion to cortical area V5 in the extrastriate cortex.

The first, known as beta movement, is demonstrated in the yellow-ball figure and forms the basis for electronic news ticker displays.

Werner E. Reichardt and Bernard Hassenstein have modelled it in terms of relatively simple "motion sensors" in the visual system, that have evolved to detect a change in luminance at one point on the retina and correlate it with a change in luminance at a neighbouring point on the retina after a short delay.

[11] Second-order mechanisms have poorer temporal resolution and are low-pass in terms of the range of spatial frequencies to which they respond.

(The notion that neural responses are attuned to frequency components of stimulation suffers from the lack of a functional rationale and has been generally criticized by G. Westheimer (2001) in an article called "The Fourier Theory of Vision.")

As in other aspects of vision, the observer's visual input is generally insufficient to determine the true nature of stimulus sources, in this case their velocity in the real world.

There are indications that the brain uses various cues, in particular temporal changes in disparity as well as monocular velocity ratios, for producing a sensation of motion in depth.

Motion in depth based on inter-ocular velocity differences can be tested using dedicated binocularly uncorrelated random-dot kinematograms.

[17][18] Additionally, as monocular cue, also the changing size of retinal images contributes to motion in depth detection.

[19] A cognitive map is a type of mental representation which serves an individual to acquire, code, store, recall, and decode information about the relative locations and attributes of phenomena in their spatial environment.

The study of directionally selective units began with a discovery of such cells in the cerebral cortex of cats by David Hubel and Torsten Wiesel in 1959.

Following the initial report, an attempt to understand the mechanism of directionally selective cells was pursued by Horace B. Barlow and William R. Levick in 1965.

[28] Their in-depth experiments in rabbit's retina expanded the anatomical and physiological understanding of the vertebrate visual system and ignited the interest in the field.

Alexander Borst and Thomas Euler's 2011 review paper, "Seeing Things in Motion: Models, Circuits and Mechanisms".

[29] discusses certain important findings from the early discoveries to the recent work on the subject, coming to the conclusion of the current status of the knowledge.

According to Barlow and Levick (1965), the term is used to describe a group of neurons that "gives a vigorous discharge of impulses when a stimulus object is moved through its receptive field in one direction.

In order to confirm that the Reichardt-Hassenstein model accurately describes the directional selectivity in the retina, the study was conducted using optical recordings of free cytosolic calcium levels after loading a fluorescent indicator dye into the fly tangential cells.

The fly was presented uniformly moving gratings while the calcium concentration in the dendritic tips of the tangential cells was measured.

It also showed that the DS property of retinal ganglion cells is distributed over the entire receptive field, and not limited to specific zones.

They used this to support their hypothesis that discrimination of sequences gives rise to direction selectivity because normal movement would activate adjacent points in a succession.

[28] ON/OFF DS ganglion cells can be divided into 4 subtypes differing in their directional preference, ventral, dorsal, nasal, or temporal.

The neurons that were preferentially responsive to vertical motion were indeed shown to be selectively expressed by a specific molecular marker.

The DS ganglion cells respond to their preferred direction with a large excitatory postsynaptic potential followed by a small inhibitory response.

[29] In addition to spatial offset due to GABAergic synapses, the important role of chloride transporters has started to be discussed.

[34] Recent research (published March 2011) relying on serial block-face electron microscopy (SBEM) has led to identification of the circuitry that influences directional selectivity.

This new technique provides detailed images of calcium flow and anatomy of dendrites of both starburst amacrine (SAC) and DS ganglion cells.

By comparing the preferred directions of ganglion cells with their synapses on SAC's, Briggman et al. provide evidence for a mechanism primarily based on inhibitory signals from SAC's[35] based on an oversampled serial block-face scanning electron microscopy study of one sampled retina, that retinal ganglion cells may receive asymmetrical inhibitory inputs directly from starburst amacrine cells, and therefore computation of directional selectivity also occurs postsynaptically.

An acetylcholine (ACh) transmission model of directionally selective starburst amacrine cells provides a robust topological underpinning of a motion sensing in the retina.

The dorsal stream (green) and ventral stream (purple) are shown. They originate from a common source in visual cortex. The dorsal stream is responsible for detection of location and motion.
Example of Beta movement , often confused with phi phenomenon , in which a succession of still images gives the illusion of a moving ball [ 5 ]
Demonstration of phi phenomenon using two black bars ( SOA = 102 ms, ISI = −51 ms)
The aperture problem. The grating appears to be moving down and to the right, perpendicular to the orientation of the bars. But it could be moving in many other directions, such as only down, or only to the right. It is impossible to determine unless the ends of the bars become visible in the aperture.
Reichardt model