the test-person shows interest. If a person is asked to focus on an object’s motion, an area corresponding to V5 is mainly activated. Paying attention to the color, an area corresponding to V4 is principally responsive. When shape is the focus, greatest activation is elsewhere along the “what” processing stream. In another task, photos of faces in frames were shown. Asking whether the faces looked different, ITC was strongly activated. Requesting whether a face was positioned symmetrically in the frame, activation shifted to the PPC.
Does imagination reactivate processes involved in visual perception?
Studies from neuroimaging in humans suggest that during visual imagination of an object, a “protocol” of the neurons operating during visual perception of that object is reactivated. Ishai and Sagi (1995) discuss common mechanisms of visual perception and visual imagination. This explains, for example, why humans with lesions in an area corresponding to V4 are unable both to recognize and imagine colors.
A different phenomenon of imagination is sensing a stimulus that actually affects another person. You see a child touching a hot stove and you will feel pain, caused by activity in appropriate structures of your brain. This kind of compassion is mediated by so-called mirror neurons (for details see Chapter 5).
Sensory maps shrink or expand depending on supply and demand
Sensory space is represented in the brain by topographic maps. From lesion and regeneration studies in amphibians it is known that the visual map of the retina in the optic tectum can be either compressed or expanded depending on the available tectal room and on the disposable retinal input. For example, if in a frog half of the retina of one eye is destroyed, a blown-up map of the remaining retina will regenerate in the entire contralateral tectum (Udin 1977).
Although such regeneration capability is not conferable to mammals, sensory cortical maps, too, may expand or shrink depending on the available cortical space and the need for perceptual skills. The phenomenon is called functional remodeling. Studies applying neuroimaging showed in the somatosensory cortex of string instrument players an expansion of the representation of the active digits to the detriment of the less active thumb (Elbert et al. 1995).
Universal potential of neural networks allows sensory substitution
The fact that underemployed cortical regions take over functions of overemployed regions is documented by neuroimaging in people blind from early age. Their visual cortex is activated by tactually reading Braille or embossed Roman letters or by other tactile discrimination tasks. Evidence of this sensory substitution was provided by transient disruption of the visual cortex by means of transcranial magnetic stimulation TMS. This induced errors in tactual discrimination tasks and distorted tactile perception in blind, but not in sighted test subjects (Cohen et al. 1997). Blindness causes the visual cortex to be recruited to a role in somatosensory processing, which contributes to the superior tactile perceptual talents of blind people.
Convergence of different sensory channels implies crossmodal interactions. In humans and most animals, a sudden touch to the body can enhance vision near that body part. Actually, cutaneous stimulation facilitates visual responses in the visual cortex (Cohen et al. 1997; Macaluso et al. 2000).
The notion that neural structures may have a “universal potential” is also in line with the fact that a perceptual principle may be implemented in different neural structures. “Lateral inhibition”—a principle by which contrast-borders are highlighted—discovered in the compound eye of the horseshoe crab, Limulus (Hartline 1949), is such a principle that works also in visual and tactile perception in vertebrates. The features-relating-algorithm—a principle of prey-selection—realized in the brains of toad (amphibian), mudskipper (fish), and mantis (insect) provides another example.
SUMMARY AND CONCLUSIONS
The examples and comparisons across various sense modalities and species we have reviewed show that perceptual worlds are shaped up to the nature of the sensory systems which in turn are adapted and adaptable to behaviorally relevant stimuli. No matter what the sensory world looks like, the orientation and communication in that world requires basic strategies of stimulus perception involving recognition and localization. The employed tactics take advantage of individual experience as well as peculiarities that emerged during evolution of the species in dependence on the ecological benefits and constraints.
Animals—including humans—tend to abstract objects in terms of configurational features. The resulting sign-stimulus elicits an assigned behavior that depends on motivation and attention. Sign-stimuli are as simple as possible and resemble the originals as closely as necessary. They facilitate both perception and communication, thereby minimizing misinterpretations between “sender” and “receiver.” Neurobiological instruments underlying stimulus perception range from specialized receptor cells in sense organs to feature-analyzing assemblies of cells and feature-detecting cells in the CNS. Certain assemblies may function in a manner of a sensorimotor-coded releasing system, that depending on motivation and attention, selects the appropriate behavior.
For most sensory modalities there are sensory brain maps containing populations of neurons selectively tuned to different stimulus features, feature combinations or configurations. Neurosensory networks may be omnipotent in that they display various degrees of plasticity involving remodeling, sensory substitution, crossmodal interaction, and learning.
FURTHER READING
Textbooks
The Study of Instinct by Tinbergen (1951) is a classic textbook of ethology—especially impressive in view of Tinbergen’s foresight, e.g., in terms of the neuroethological fundamentals of behavior.
Hogan (2017) provides new insights in the study of animal behavior including behavioral ecology, neuroscience, cognitive psychology, and evolutionary developmental biology.
Prete (2004) presents a multi-author textbook describing in depth what the perceptual worlds of animals of various species might be.
Readers interested in the research of olfactory perception in insects will enjoy the ambitious review by Kaissling (2014).
Carew (2004) and Zupanc (2019) provide the best up-to-date treatments of neuroethology.
Movies
Ewert, J.-P. & IWF (Institut für den Wissenschaftlichen Film, Göttingen). Voice-Over: English.
If you scan this QR code with the QR app of your smartphone, or click the URL, you’re directed to an internet TIB|AV-Portal, which allows you to watch three English versions of movies about the visually guided prey-catching and threat-avoidance behaviors in toads and the underlying neurophysiological processes.
A1: Image Processing in the Visual System of the Common Toad: Behavior, Brain Function, Artificial Neuronal Net (No.: C1805). https://av.tib.eu/media/15148
This weblink refers to the movie dealing with: Image processing in the toad’s visual system from behavior to brain function, which is explained by a global model (“window hypothesis”) and simulated
