title: Ultra-rapid categorization of fourier-spectrum equalized natural images: macaques and humans perform similarly.
abstract: BACKGROUND
  Comparative studies of cognitive processes find similarities between humans and apes but also monkeys. Even high-level processes, like the ability to categorize classes of object from any natural scene under ultra-rapid time constraints, seem to be present in rhesus macaque monkeys (despite a smaller brain and the lack of language and a cultural background). An interesting and still open question concerns the degree to which the same images are treated with the same efficacy by humans and monkeys when a low level cue, the spatial frequency content, is controlled.
  
  
  RESULTS
  We used a set of natural images equalized in Fourier spectrum and asked whether it is still possible to categorize them as containing an animal and at what speed. One rhesus macaque monkey performed a forced-choice saccadic task with a good accuracy (67.5% and 76% for new and familiar images respectively) although performance was lower than with non-equalized images. Importantly, the minimum reaction time was still very fast (100 ms). We compared the performances of human subjects with the same setup and the same set of (new) images. Overall mean performance of humans was also lower than with original images (64% correct) but the minimum reaction time was still short (140 ms).
  
  
  CONCLUSIONS
  Performances on individual images (% correct but not reaction times) for both humans and the monkey were significantly correlated suggesting that both species use similar features to perform the task. A similar advantage for full-face images was seen for both species. The results also suggest that local low spatial frequency information could be important, a finding that fits the theory that fast categorization relies on a rapid feedforward magnocellular signal.
authors.affiliation: Université de Toulouse, UPS, Centre de Recherche Cerveau et Cognition (CerCo), Toulouse, France. pascal.girard@cerco.ups-tlse.fr
authors.forename: Pascal
authors.initials: P
authors.lastname: Girard
authors.forename: Roger
authors.initials: R
authors.lastname: Koenig-Robert
mesh_terms: D000818:Animals; D002965:Classification / Q000379:methods; D003463:Cues; D005260:Female; D006801:Humans; D008251:Macaca / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D011856:Radiographic Image Enhancement; D011930:Reaction Time / Q000502:physiology; D012438:Saccades / Q000502:physiology; D017550:Spectroscopy, Fourier Transform Infrared; D013647:Task Performance and Analysis; D013997:Time Factors; D014796:Visual Perception / Q000502:physiology