In philosophy, psychology, and cognitive science, perception is the organization, identification, and interpretation of sensory information in order to represent and understand the environment. All perception involves signals in the nervous system, which in turn result from physical or chemical stimulation of the sense organs. For example, vision involves light striking the retina of the eye, smell is mediated by odor molecules, and hearing involves pressure waves. Perception is not the passive receipt of these signals, but is shaped by learning, memory, expectation, and attention.

Perception can be split into two processes. Firstly, processing sensory input, which transforms these low-level information to higher-level information (e.g., extracts shapes for object recognition). Secondly, processing which is connected with a person's concepts and expectations (knowledge) and selective mechanisms (attention) that influence perception.

Perception depends on complex functions of the nervous system, but subjectively seems mostly effortless because this processing happens outside conscious awareness.

Since the rise of experimental psychology in the 19th Century, psychology's understanding of perception has progressed by combining a variety of techniques. Psychophysics quantitatively describes the relationships between the physical qualities of the sensory input and perception.

Sensory neuroscience studies the brain mechanisms underlying perception. Perceptual systems can also be studied computationally, in terms of the information they process. Perceptual issues in philosophy include the extent to which sensory qualities such as sound, smell or color exist in objective reality rather than in the mind of the perceiver.

Although the senses were traditionally viewed as passive receptors, the study of illusions and ambiguous images has demonstrated that the brain's perceptual systems actively and pre-consciously attempt to make sense of their input. There is still active debate about the extent to which perception is an active process of hypothesis testing, analogous to science, or whether realistic sensory information is rich enough to make this process unnecessary.

The perceptual systems of the brain enable individuals to see the world around them as stable, even though the sensory information is typically incomplete and rapidly varying. Human and animal brains are structured in a modular way, with different areas processing different kinds of sensory information. Some of these modules take the form of sensory maps, mapping some aspect of the world across part of the brain's surface. These different modules are interconnected and influence each other. For instance, taste is strongly influenced by smell.

Perception is one of the oldest fields in psychology. The oldest quantitative law in psychology is the Weber-Fechner law, which quantifies the relationship between the intensity of physical stimuli and their perceptual effects. The study of perception gave rise to the Gestalt school of psychology, with its emphasis on holistic approach.

What one perceives is a result of interplays between past experiences, including one's culture, and the interpretation of the perceived. Read more

In the News ...

When your eyes override your ears: New insights into the McGurk Effect   Science Daily - February 16, 2017

New model shows how the brain combines information from multiple senses. Seeing is not always believing -- visual speech (mouth movements) mismatched with auditory speech (sounds) can result in the perception of an entirely different message. This mysterious illusion is known as the McGurk Effect. Neuroscience researchers have created an algorithm to reveal key insight into why the brain can sometimes muddle up one of the most fundamental aspects of the human experience.

Fractal edges shown to be key to imagery seen in Rorschach inkblots   Science Daily - February 14, 2017

Researchers have unlocked the mystery of why people have seen so many different images in Rorschach inkblots. The image associations are induced by fractal characteristics at the edges of the blots and depend on the scaling parameters of the patterns, says researcher. Fractals are objects with irregular curves or shapes and are recognizable building blocks of nature. Trees, clouds, rivers, galaxies, lungs and neurons are fractals. The new discovery isn't about improving inkblots for psychological assessments -- their use became controversial and mostly set aside in the last 20 years. It does, however, have implications for Taylor's efforts to design a fractal based retinal implant and for potentially improving materials used for camouflage.

How does the brain make perceptual predictions over time?   Medical Express - February 6, 2017
Prediction is crucial for brain function - without forecasting, our actions would always be too late because of the delay in neural processing. However, there has been limited theoretical work explaining how our brains perform perceptual predictions over time. Prediction may be a general principle of cortical function along with the already-established role of inference. Largely missing from our understanding of brain function had been models akin to those routinely employed by meteorologists. In making their predictions, forecasters rely on past weather information to project climate conditions over the next several days. Similarly, the neural networks in our brains embody a type of model of our surroundings. However, we don't have a clear understanding of how they operate to make predictions. Existing theories of brain function and neural networks used in artificial intelligence use a hierarchical structure: sensory input comes in at one end and progressively more abstract representations are computed along the hierarchy.

Remembrance of things future: Long-term memory sets the stage for visual perception   Medical Express - December 28, 2011
Rather than being a passive state, perception is an active process fueled by predictions and expectations about our environment. In the latter case, memory must be a fundamental component in the way our brain generates these precursors to the perceptual experience - but how the brain integrates long-term memory with perception has not been determined.

Time on the Brain: How You Are Always Living In the Past, and Other Quirks of Perception   Scientific American - September 20, 2011
Neuroscientist Kathleen McDermott of Washington University began by quoting famous memory researcher Endel Tulving, who called our ability to remember the past and to anticipate the future mental time travel. You don't use the phrase time travel lightly in front of a group of physicists for whom the concept is not a convenient metaphor but a very real possibility. But when you hear about how our minds glide through time - and how our memory provides a link not only to the past but also to the future - you see Tulving's point.

Sad People Have Surprising Memory Advantage   Live Science - August 21, 2011
Sad people are apparently better than happy people at face recognition, an upside to being down in the dumps that is yielding insights into how mood can affect the brain. The findings, based on experiments involving college students, could help lead to better treatments for depression, psychologists say. Past studies have found that unhappiness is often detrimental to a wide range of mental tasks, such as abstract thinking and remembering lists of words. A number of researchers had attributed this to brooding deeply and elaborately about one's surroundings, while others thought it might be due to being distracted by one's own concerns.

Cognitive neuroscientists shed light on how the brain responds to scenes and their mirror-image reversals   PhysOrg - August 18, 2011
New research suggests that some parts of the brain perceive a scene and its mirror image as one and the same, meaning those regions are involved in scene categorization rather than navigation. Picture a penny. You can probably recall its color (copper), which historical figure graces its front (Abraham Lincoln), and even the orientation of the portrait (profile, as opposed to straight on). But can you remember which way Lincoln is facing? According to MIT research scientist Daniel D. Dilks, only about half of us get this right, meaning we're performing no better than if we had simply guessed. This well-known phenomenon suggests that left-right distinctions are irrelevant to object recognition; in other words, our brains perceive an object and its mirror image as one and the same.

Illusion Reveals How Brain Adapts to Motion   Live Science - July 1, 2011
Watch something in motion, say, a waterfall or scrolling text on a video game, then look away at a rock, a wall, or anything stationary. Briefly, the stationary object will appear to move in the opposite direction. This visual illusion has been recognized for a very long time; Aristotle first noted it. Now, a new study has found that even a very brief glimpse of motion - for as little as 1/40 of a second - can trigger the brain mechanism responsible for the illusion.

Missing the gorilla: Why we don't see what's right in front of our eyes   PhysOrg - April 18, 2011
University of Utah psychologist Jason Watson displays a famous video showing people passing a basketball while a person in a gorilla suit walks across the screen. When unsuspecting viewers were asked to count how many times the basketball is passed, more than 40 percent failed to see the person in the gorilla suit.

Scientists find evidence for 'chronesthesia,' or mental time travel   PhysOrg - December 22, 2010
Researchers have found evidence for chronesthesia, which is the brain's ability to be aware of the past and future, and to mentally travel in subjective time. They found that activity in different brain regions is related to chronesthetic states when a person thinks about the same content during the past, present, or future.

New study debunks myth about popular optical illusion   PhysOrg - December 21, 2010
A psychology professor has found that the way people perceive the Silhouette Illusion, a popular illusion that went viral and has received substantial online attention, has little to do with the viewers' personality, or whether they are left- or right-brained, despite the fact that the illusion is often used to test these attributes in popular e-quizzes.

How the brain's architecture makes our view of the world unique   PhysOrg - December 6, 2010
The Ebbinghaus Illusion. Most people will see the first circle as smaller than the second one Researchers found a strong link between the surface area of the primary visual cortex and the extent to which volunteers perceived the size illusion -- the smaller the area, the more pronounced the visual illusion.

Now You See It: Neuroscientists Reveal Magicians' Secrets   Live Science - December 6, 2010
Magicians create illusions by taking advantage of how we perceive stimuli and process information. For example, a dove fluttering from a hat can be used to draw an audience's attention away from the actual trick. There is a place for magic in science. Five years ago, on a trip to Las Vegas, neuroscientists Stephen Macknik and Susana Martinez-Conde realized that a partnership was in order with a profession that has an older and more intuitive understanding of how the human brain works. Magicians, it seems, have an advantage over neuroscientists.