Recognition of natural objects in the archerfish

Object identity representation occurs early in the archerfish visual system

Archerfish hunt by shooting a jet of water at aerial targets, a behavior used to study their visual processing by presenting a set of images on a screen above the water tank and observing the behavioral response. Building on this unique behavior, it was recently shown that archerfish can be trained to distinguish between different object categories by generalizing from examples. Analysis of the archerfish's behavior revealed that the fish visual system relies on a small set of visual features for categorization and is more sensitive to object contours than to textures. To understand the neural basis of this object recognition, we investigated the neural representation of features and objects in the archerfish optic tectum using recording of single cells. We found that, although the optic tectum is an early stage of visual processing, a small population of neurons in this region contains information about the object category. This contrasts with the primate visual system, where the representation of objects emerges only at later stages of visual processing. These results suggest that early-stage feature extraction and object categorization in archerfish might represent a form of specialized visual processing. This contributes to a broader understanding of visual processing across taxa.

An evolutionarily distinct Hmgn2 variant influences shape recognition in Medaka Fish

Protein sequence diversification significantly impacts physiological traits. In this study, using medaka fish (Oryzias latipes), we identify a novel protein variant affecting shape preference behavior. Re-analysis of sequencing data reveals that LOC101156433 encodes a unique Hmgn2 variant with unusual subnuclear localization, clustered separately from the Hmgn2 clades of other species. Medaka mutants with this variant showed reduce telencephalic regions and altered shape preference, suggesting a link between protein sequence variation and behavioral changes. Additionally, this Hmgn2 variant is common in Acanthopterygii fishes, which are adapted to a variety of environments, indicating its potential evolutionary significance. Our findings highlight the relationship between amino acid sequence variation and the development of new molecular and behavioral adaptations, providing insights into the visual shape perception system in fish.

The archerfish uses motor adaptation in shooting to correct for changing physical conditions

The archerfish is unique in its ability to hunt by shooting a jet of water from its mouth that hits insects situated above the water's surface. To aim accurately, the fish needs to overcome physical factors including changes in light refraction at the air-water interface. Nevertheless, archerfish can still hit the target with a high success rate under changing conditions. One possible explanation for this extraordinary ability is that it is learned by trial and error through a motor adaptation process. We tested this possibility by characterizing the ability of the archerfish to adapt to perturbations in the environment to make appropriate adjustments to its shots. We introduced a perturbing airflow above the water tank of the archerfish trained to shoot at a target. For each trial shot, we measured the error, i.e., the distance between the center of the target and the center of the water jet produced by the fish. Immediately after the airflow perturbation, there was an increase in shot error. Then, over the course of several trials, the error was reduced and eventually plateaued. After the removal of the perturbation, there was an aftereffect, where the error was in the opposite direction but washed out after several trials. These results indicate that archerfish can adapt to the airflow perturbation. Testing the fish with two opposite airflow directions indicated that adaptation took place within an egocentric frame of reference. These results thus suggest that the archerfish is capable of motor adaptation, as indicated by data showing that the fish produced motor commands that anticipated the perturbation.

Figure-ground segmentation based on motion in the archerfish

Figure-ground segmentation is a fundamental process in visual perception that involves separating visual stimuli into distinct meaningful objects and their surrounding context, thus allowing the brain to interpret and understand complex visual scenes. Mammals exhibit varying figure-ground segmentation capabilities, ranging from primates that can perform well on figure-ground segmentation tasks to rodents that perform poorly. To explore figure-ground segmentation capabilities in teleost fish, we studied how the archerfish, an expert visual hunter, performs figure-ground segmentation. We trained archerfish to discriminate foreground objects from the background, where the figures were defined by motion as well as by discontinuities in intensity and texture. Specifically, the figures were defined by grating, naturalistic texture, and random noise moving in counterphase with the background. The archerfish performed the task well and could distinguish between all three types of figures and grounds. Their performance was comparable to that of primates and outperformed rodents. These findings suggest the existence of a complex visual process in the archerfish visual system that enables the delineation of figures as distinct from backgrounds, and provide insights into object recognition in this animal.