Perception

A small study has tested the eminent Donald Hebb’s hypothesis that visual imagery results from the reactivation of neural activity associated with viewing images, and that the re-enactment of eye-movement patterns helps both imagery and neural reactivation.

The olfactory bulb is in the oldest part of our brain. It connects directly to the amygdala (our ‘emotion center’) and our prefrontal cortex, giving smells a more direct pathway to memory than our other senses. But the olfactory bulb is only part of the system processing smells. It projects to several other regions, all of which are together called the primary olfactory cortex, and of which the most prominent member is the piriform cortex.

Previous research has found practice improves your ability at distinguishing visual images that vary along one dimension, and that this learning is specific to the visual images you train on and quite durable. A new study extends the finding to more natural stimuli that vary on multiple dimensions.

Here’s a perception study with an intriguing twist. In my recent round-up of perception news I spoke of how images with people in them were more memorable, and of how some images ‘jump out’ at you. This study showed different images to each participant’s left and right eye at the same time, creating a contest between them. The amount of time it takes the participant to report seeing each image indicates the relative priority granted by the brain.

Memory begins with perception. We can’t remember what we don’t perceive, and our memory of things is influenced by how we perceive them.

Our ability to process visual scenes has been the subject of considerable research. How do we process so many objects? Some animals do it by severely limiting what they perceive, but humans can perceive a vast array of features. We need some other way of filtering the information. Moreover, it’s greatly to our advantage that we can process the environment extremely quickly. So that’s two questions: how do we process so much, and so fast?

Our common difficulty in recognizing faces that belong to races other than our own (or more specifically, those we have less experience of) is known as the Other Race Effect. Previous research has revealed that six-month-old babies show no signs of this bias, but by nine months, their ability to recognize faces is reduced to those races they see around them.

An experiment with congenitally deaf cats has revealed how deaf or blind people might acquire other enhanced senses. The deaf cats showed only two specific enhanced visual abilities: visual localization in the peripheral field and visual motion detection. This was associated with the parts of the auditory cortex that would normally be used to pick up peripheral and moving sound (posterior auditory cortex for localization; dorsal auditory cortex for motion detection) being switched to processing this information for vision.

We can see shapes and we can feel them, but we can’t hear a shape. However, in a dramatic demonstration of just how flexible our brain is, researchers have devised a way of coding spatial relations in terms of sound properties such as frequency, and trained blindfolded people to recognize shapes by their sounds. They could then match what they heard to shapes they felt. Furthermore, they were able to generalize from their training to novel shapes.

As I get older, the question of how we perceive speech becomes more interesting (people don’t talk as clearly as they used to!). So I was intrigued by this latest research that reveals that it is not so much a question of whether consonants or vowels are more important (although consonants do appear to be less important than vowels — the opposite of what is true for written language), but a matter of transitions.