title: Pupil response triggered by the onset of coherent motion.
abstract: BACKGROUND
  Recent studies have shown that transient constrictions of the pupil can be elicited by visual stimuli that do not cause an increment in light flux level on the retina. Such stimuli include achromatic gratings and isoluminant chromatic patterns.
  
  
  METHODS
  We investigated pupillary responses to the onset of coherent movement generated in a pattern of dots in random motion. Measurements were carried out in normal observers and in a subject with hemianopia caused by damaged primary visual cortex.
  
  
  RESULTS
  The experimental findings show that the onset of coherent motion triggers systematic constrictions of the pupil that cannot be accounted for in terms of a pupil light reflex response. We labelled these constrictions Pupil motion responses (PMRs). Results show that PMRs have large response latencies and on average are of small response amplitudes. The dependence of PMRs on changes in motion parameters such as stimulus speed and direction of motion has been investigated.
  
  
  CONCLUSIONS
  The existence of PMRs to the onset of the coherent motion in human vision has been demonstrated. These new findings are discussed in relation to the psychophysical and physiological data on motion perception and the possible pathways involved in the control of the pupil response.
authors.affiliation: Department of Optometry and Visual Science, City University, London, UK. A.Sahraie@city.ac.uk
authors.forename: A
authors.initials: A
authors.lastname: Sahraie
authors.forename: J L
authors.initials: JL
authors.lastname: Barbur
mesh_terms: D006423:Hemianopsia / Q000503:physiopathology; D006801:Humans; D009039:Motion Perception / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology; D010775:Photic Stimulation; D011680:Pupil / Q000502:physiology*; D012025:Reflex, Pupillary; D014793:Visual Cortex / Q000502:physiology