Universality shown in visual search by fish and humans

Researchers have shown that the way fish perform visual searches resembles the way humans do and provides an important insight in to the way the visual system works.

April 26, 2015 01:39
4 minute read.

Fish (illustrative). (photo credit: ING IMAGE/ASAP)


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Surprisingly, fish and humans have an important brain function in common. Ben-Gurion University of the Negev researchers have shown that the way fish perform visual searches resembles the way humans do and provides an important insight in to the way the visual system works.

Visual search – the ability to find an object of interest against a background – is a task humans encounter on a daily basis. When looking for a car in the parking lot or searching for a key among the many items on a desk, we rely on visual features that can distinguish the object of interest from its surroundings. For animals, from detecting food items to locating lurking predators, this ability has to be accurate and fast to ensure survival.

In mammals, including humans, the need for fast visual search led to the development of an important brain capability that enables the scanning of the visual scene in a parallel fashion – a concurrent processing of the entire visual scene as opposed to serial processing of object by object.

This ability, called “pop-out visual search,” makes it possible for the observer to rapidly detect the object of interest. Pop-out search is believed to be based on a population of brain cells that together generate a map that analyzes every location in the visual scene to determine how different it is from its surroundings. This map simplifies the representation of the visual field and highlights the location which differs the most from its nearby regions. During casual viewing, the observer’s attention is drawn toward this location. Over the years, much work has been devoted to showing that these specialized brain cells are located in the cortex, which is the largest and most recently evolved area in the mammalian brain.

At present, most research has focused on monkeys and humans to study visual search. But studying an animal that is an earlier evolutionary life form can offer a new perspective on understanding the human brain by exploring the evolutionary and developmental perspectives of important behaviors.

In a recent study published in Nature Communications, the BGU group followed this approach and focused on the archer fish, which lacks a fully developed cortex.

This species of fish exhibits complex visual hunting behavior, as it shoots down prey found on foliage above water level and is able to learn to distinguish between artificial targets presented on a computer monitor in an experimental setting. The BGU researchers headed by Prof. Ronen Segev of the life sciences department have levered this exceptional visual behavior to study visual search in the lower vertebrate.

The archer fish, as this study reveals, exhibits a popout visual search mode of moving targets; it was able to detect a target that moved faster than the other objects presented on the screen. Importantly, this detection was not affected by the number of objects in the display, an indicative property of pop-out. This is the first evidence for pop-out search mode in a non-mammal and in particular, non-primate.

To understand the computation needed for this behavior in the archer fish brain, the researchers recorded the activity of the brain cells from the optic tectum, which is the main visual area and one of the largest areas in the archer fish brain. This area also exists in primates.

But due to the massive expansion of the cortex, this area comprises a much smaller fraction of the primate’s brain. The new study shows that the activity patterns of the archer fish brain cells are similar to those found in the mammalian visual cortex. This implies that the visual cortex may not be the crucial component in generating the map of the unique locations in the visual field.

The scientists were able to show that the pop-out search mode exists in fish – and this could indicate that the parallel search mode may be a common, and perhaps even universal, mechanism across vertebrates’ visual systems.

‘HISTORIC’ COOPERATIVE AGREEMENT A new partnership between the University of Haifa and the Israel Oceanographic and Limnological Research Institute will advance deep sea research in Israel, according to the two bodies. As part of the first cooperative venture of its kind between them, a cornerstone-laying ceremony was held launching the construction of the deep-sea research labs for the Harry and Leona Helmsley Mediterranean Sea Research Center at the university. “This is a historic partnership that will substantially advance sea research in Israel,” said university president Amos Shapira.

They are cooperating in the framework of the Mediterranean Sea Research Center of Israel (MERCI), which was established in 2012 and led by the University of Haifa.

MERCI is a consortium of all of Israel’s research universities, two government research institutes and an academic college. As part of this new cooperative venture, university laboratories are to be built on IOLR grounds to create synergy between the researchers and research equipment at IOLR and the researchers and research equipment that the university will install in the new deep-sea research labs, which are being funded by the Leona and Harry Helmsley Charitable Trust and other sources.

The facility will include a lab for unmanned underwater vehicles; an engineering and research pool; an optics laboratory to develop and test underwater vision systems; an acoustics lab for sonar systems; an underwater propulsion laboratory to develop underwater propulsion devices and systems; and a marine diving workshop. These will be the first labs of their type in this country, and underwater robots, unmanned submarines, advanced underwater sensing devices and other systems will be purchased.

MERCI director Prof. Zvi Ben Avraham noted that the combination of a research university and oceanographic institute is the world’s leading model for marine research. “We will make the research infrastructure we are building today available to the entire scientific community in Israel and neighboring countries,” he said.

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