Seeing Straight and Responding Quickly: Peripheral vs. Central Vision

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Updated on Jan 13, 2014

Grade Level: Middle School ;Type: Life science


  • Discover how quickly our fingers respond to what our eyes see
  • Learn the anatomical and physiological differences between central and peripheral visual systems
  • Learn about the functions of the photopic vs. scotopic systems

Research Questions:

  • What are that reaction times are faster when subjects are looking directly at the stimulus with their photopic system than when they are looking indirectly at the stimulus with their scotopic systems?
  • What are the advantages of the scotopic system?
  • What, besides speed of reaction, are some of the advantages of the photopic system?

How quickly do our fingers respond to what our eyes see? Before launching this experiment, you should try to learn about the anatomy and physiology of the central (photopic) and peripheral (scotopic) visual systems. You will test the subjects’ visual reaction times using each of these systems.


  • Use of a computer
  • A computer program that can be accessed for $9.95 for three months, which you will find here
  • Create a data sheet by drawing three vertical columns. Label the first one “Subject #”, the second one, "Reaction Time/Central Vision”, and the third, “Reaction Time/Peripheral Vision”

Experimental Procedure

  1. Research the anatomy and physiology of the central (photopic) and peripheral (scotopic) visual systems.
  2. Sign up for access to the visual reaction time program at this website.
  3. Test subjects one at a time (run as many subjects as possible; 30 is ideal). Have the subject read the test instructions on the computer screen and in addition give him/her the following instructions: “You will be engaging in a visual reaction time task in which you will be presented with a vertical display of lights much like a traffic signal. You will be instructed to press the ‘down arrow’ as quickly as possible when the light changes from red to green, then to release it and prepare for the next trial. If you press the key before the light turns green, it will count as an error. Your task will be completed when you have responded correctly 20 times and your average reaction time will be recorded. You will perform two sets of trials, one in which you are looking directly at the light tree, and another in which you are focused on the edge of the computer screen and seeing the light tree your peripheral vision.”
  4. Tell the subject whether s/he will be participating in the central or peripheral task first. For the central task, instruct the subject to look directly at the light tree. For the peripheral task, instruct the subject to look at the edge of the computer screen. Record the reaction times for both tasks.
  5. Average the average reaction times across subjects for both the central and the peripheral tasks.
  6. Graph the results and discuss them in terms of the anatomy and physiology of the central (photopic) versus peripheral (scotopic) visual systems.

Terms/Concepts: Photopic visual system; Scotopic visual system ; Cones; Rods; Fovea


Dr. LaCerra is an evolutionary neuroscientist, author of âThe Origin of Mindsâ (with co-author, Roger Bingham, Harmony, 2002) and a columnist and contributing editor at âSpirituality & Healthâ Magazine.

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