Fast Categorization in monkeys and humans

Task and Constraints

Visual Categorization of natural images by humans and monkeys (A)

Animal / Non Animal (Target = Animal) or Food / Non Food (Food = target)

Central brief presentation: 30ms - No time for eye movement

Go / No-go Response

• Target: Release button (C) and touch screen (B) in under 1s
• Distractor: keep pressing button for 1s (C)

Response to the first presentation of a new image - no learning

Data Bank: 40 000 images

Commercialized CDrom

Large variety of photographs

Minimized effect of context

No a priori information about

• Target or distractor
• Type of target
• Size, Number, View or Position

Images in the food task	Images in the animal task

Categorization of B&W and Color images in monkeys and humans

Both Monkeys and Humans subjects

Previously unseen B&W natural scenes mixed with color ones
 
The faster the subject, the less he uses color cues (see figure below). Monkeys behave as fast human subjects

(published in Vision Research see publication)

Categorization of familiar images versus previously unseen ones

For Monkeys, it's part of their training process.

For humans a special protocol had been set up in which they had to categorize the same 200 images for 15 consecutive days. Then these images were mixed with 1200 previously unseen ones to asses the difference between familiar and new images.

Very surprisingly, for images categorized in under 250ms in humans (respectively 200ms in monkeys) they were no significant difference between familiar and new images. Moreover for humans, early ERPs for familiar and new images were hardly distinguishable (see figure below).