Independent and Dependent Variables Used

¶ … independent and dependent variables used in the first experiment; include the levels of each variable. (maximum 2 sentences,

The independent variable used by Snowden in his experiment Visual Attention to Color is the arrangement of color cue stimuli presented as dynamic random noise patches centered along either side of a fixation cross. The dependent variable is the participant's varying processes of attentional guidance based on cues containing only color information, manifested by the exogenous control of visual attention, as measured by their reaction times during mouse click responses to color cue stimuli.

Are there any methodological flaws or limitations in the experimental design? Explain.

While Snowden and his research team undoubtedly dedicated much of their focus to designing a thorough and rigorous experiment, as evidenced by the detailed mathematical measurement process described in the Methods section, the effect of certain methodological flaws and limitations on his results must be considered. The primary methodological limitation observed in Snowden's experimental design is the extremely small sample size studied, as only eight (8) individuals were included as participants in the study. By examining the effects of color cues on P. stream attentional guidance, which is a precise and intricate set of experimental parameters, through such a small sample size, Snowden has rendered his conclusions vulnerable to valid criticism which holds that his findings may simply represent statistical noise or random variation.

3.) How did the experimenters control for possible confounding variables?

Within the confines of Snowden's particular experimental design, the most likely confounding variable to potentially cause adverse measurable effects was that of luminescence information, as the goal of this study was to assess attentional guidance to visual cues containing only color information. As he was highly cognizant of the threat that luminescence information could pose to the validity of his results, Snowden observed that "one way of eliminating luminance artifacts is to embed the stimuli in random luminance noise that makes any small remaining differences in luminance invisible, and also serves to mask any high-spatial-frequency artifacts" (181), before describing the control process of using dynamic random noise backgrounds to present trials. Snowden also had to control for the confound ding variable of visual adaption to the same image, and this was achieved by having subjects view the green screen for at least 2 minutes before the data collection began, and by adjusting the equiluminescence point to the proper level red cue display.

4.) Explain the role of the magnocellular and parvocellular streams (from what you learned from lecture or from your textbook). Explain how the research discussed in this article expands upon previous views

As Snowden observes in his article, the primate visual system is divided into at least two distinct areas on the subcortical level: the magnocellular (M) stream and the parvocellular (P) stream. Decades of investigative analysis on the construction and purpose of these visual divisions has revealed that the M. stream is adapted to process transient information, lacks the refinement to signal fine details, and is incapable of distinguishing the inputs generated by long- and medium-wavelength cones (Snowden 180). Conversely, the P. stream is assists in focusing on stationary objects, processes fine details instantaneously, and contains cells with color-opponent receptive fields. As previous experiments have demonstrated, lesions of the P. stream cause colorblindness while lesions of the M. stream have no such effect, and when one considers that color changes have typically not caused attentional capture in studies, this distinction suggests that the M. stream plays the predominant role in guiding attention capture and eye movement. Snowden's research debunks this traditional conception of the role that the P. stream and M. stream play in primate vision, showing that color change signals can isolate the P. stream in the process of automatic attention capture, and that color vision is an adaptive trait designed to aid in target detection, identification, and localization.

5.) What are the implications of the authors' findings? Relate your answer to a sensation or perception topic that you have learned about in this class.

The findings presented by Snowden within his study Visual Attention to Color are extremely intriguing when one considers the history of research on M. stream/P stream activity and attentional guidance. As Snowden states in the Discussion section of his article, "the current finding appears to establish conditions under which a purely chromatic signal can automatically attract attention, and thus shows that color vision can play a vital role in the guidance of visual behavior" (183), and the implications of this result are wide-ranging in terms of their potential application to the study of color vision and colorblindness. By demonstrating that the M. stream is not strictly colorblind, Snowden has opened the doors for a new avenue of visual study, one aimed at determining the link between color vision and attentional guidance. The survival instincts that drove primates to develop the adaptive traits necessary for target detection, identification, and localization still affect many human activities, from sports and recreation to driving safely. By expanding the horizons of examination within the realm of primate visual science, Snowden has continued the progression of empirical knowledge acquisition which is essential to improving understanding of our own sensory processes.

6.) Design an experiment to test whether the parvocellular stream is sensitive to motion processing (maximum 1-page, 7 points as details below)

The following experiment is intended to examine the parvocelluar stream's sensitivity to motion processing relative to the magnocellular stream. Participants in the study will be exposed to a stimulus array containing varying levels of minutely detectable movements, ranging from nearly instantaneous shifts in position to extended movements. Their ability to perceive and respond to these movements using perceptual motion processing will be measured to determine if this phenomenon is generated within the parvocellular stream of vision, in addition to the magnocellular stream. It is expected that the inclusion of certain movement types (zig-zag, random spacing, etc.) will stimulate the parvocellular stream to effect motion processing on a perceptual level.

1.) What methods would you use? (e.g., describe your stimuli, your task, etc.)

A total of 64 subjects (32 males / 32 females) comprised of university students will participate in the study, pending a routine screening for vision defects or other anomalies which would preclude their inclusion. An array of 12 motion-based stimuli will be presented to each participant on a randomly rotating basis, with each participant viewing all 12 stimuli in random order multiple times to control for the confounding variable of cognitive expectation. The stimulus arrays will be presented via computer screens displaying static images that move in distinct ways (vertically, horizontally, diagonally, etc.), and again each array will be identical in terms of coloration, luminescence, and other visual properties that may present confounding variables. The rate of processing through which each participant reacts to the movement depicted will be measured using mouse-click response time software.