stimulus location

Thu Apr 1 12:21:20 UTC 2010

http://www.tedmontgomery.com/the_eye/acuity.html

Do the math

/Jens

On 1 Apr, 11:11, ashraf <ash2003r... at yahoo.com> wrote:
> on a 38-cm computer screen placed 60 cm away from the
> subjects.. The task display consisted of
> a circle (2.6º radius) of six letters centered at fixation, plus a
> peripheral distractor letter, presented to the left or right of the
> circle,º 4 away from fixation.. Each of the
> circle letters subtended 1.5º by º1.1 , and the distractor letter
> subtended º1.8by º1.4.
> circle contained one target, and subjects were instructed to indicate
> which of the target letters was present in the circle by
> pressing either the ‘‘0’’ or the ‘‘2’’ key on the numerical pad of the
> computer as quickly as possible .Is this radius is suitable from the
> perspective of visual acuity
>
> On 31 مارس, 12:06, Michiel Spape <Michiel.Sp... at nottingham.ac.uk>
> wrote:
>
> > Hi,
> > Okay, so the question is whether one would be able to read a 2.5 degrees letter that is placed 2.5 degrees from fixation? So, unless my calculations are horribly off, that is 2.19 cm (about an inch, for imperial readers) given a distance to the screen of about 50 cm, right (quite possibly wrong)? If I got this right, anyway, and given that you use such a large letter, I see no reason why someone wouldn't be able to read it, as long as the letter in question is Latin or a similar simple script.
>
> > Here's the relevant part of the user guide (p A-34), for those wondering:
> > "The location of the stimulus can have a powerful effect on both RT and error rates.  Visual acuity
> > drops quickly as stimuli are moved away from the fovea—the narrow area of vision straight ahead
> > that is about 2° wide.  A person with 20/20 vision in the fovea will typically have about 20/80
> > vision 2.5° from straight-ahead.  At 10° from straight ahead most people have worse than 20/300
> > vision.  To put this in perspective, at a viewing distance of 57 cm (22.5”), each centimeter is about
> > 1° of visual angle, so a letter displayed 2.5 cm (about 1”) from fixation will be seen quite poorly."
>
> > ... but that depends rather on the size of the letter - whether it is 'seen' quite poorly. Furthermore, there's plenty of paradigms where seeing things quite poorly is exactly what you'd want (subliminal or near-subliminal priming, for instance) and in other cases, eye-movements are permitted (visual search, usually). What's the paradigm you're working on?
> > Best,
> > Mich (not natively from Notts)
>
> > Michiel Spapé
> > Research Fellow
> > Perception & Action group
> > University of Nottingham
> > School of Psychology
>
> > -----Original Message-----
> > From: e-prime at googlegroups.com [mailto:e-prime at googlegroups.com] On Behalf Of ashraf
> > Sent: 30 March 2010 23:58
> > To: E-Prime
> > Subject: Re: stimulus location
>
> > I'm sorry, I'm not a native English speaker , my first Arab.
> > My question is about the suitable radius of a circle of letters to be
> > seen very well from the perspective of visual acuity.
>
> > On 30 ãÇÑÓ, 18:07, Michiel Spape <Michiel.Sp... at nottingham.ac.uk>
> > wrote:
> > > Sorry, I missed a line in there!
>
> > > "visual angle from fixation will seen Quit poorly,Is this mean ,that"
>
> > > Though it didn't really affect the conclusion.
>
> > > Michiel Spapé
> > > Research Fellow
> > > Perception & Action group
> > > University of Nottingham
> > > School of Psychology
>
> > > -----Original Message-----
> > > From: e-prime at googlegroups.com [mailto:e-prime at googlegroups.com] On Behalf Of Michiel Spape
> > > Sent: 30 March 2010 16:47
> > > To: e-prime at googlegroups.com
> > > Subject: RE: stimulus location
>
> > > Your inline would work better if you correct the syntax:
>
> > > Hi group,
> > > I read in the e-prime user guide, in appendix B on page 34 - considering the stimulus location - that displaying a circle at a visual angle of 2.5 degrees from a central fixation letter, its radius must be greater than 2.5 degrees. Otherwise, it will not be suitably large enough to study attention.
>
> > > ...but I might be completely wrong in thinking this is what you're saying. If, however, it is, the answer is, as Jens says, no. To expand on that, it makes little sense from a psychological point of view. Since I find it unlikely you were asking this, however, I'll not go much farther than Jens and will merely ask you, again, to take a course in English and/or (presumably and) install a spelling check on your system. My apologies if this sounds pedantic, I'm not being a spelling-nazi, it's just that your wording can only be understood by someone with para-semantic skills
> > > Best,
> > > Mich
>
> > > Michiel Spapé
> > > Research Fellow
> > > Perception & Action group
> > > University of Nottingham
> > > School of Psychology
>
> > > -----Original Message-----
> > > From: e-prime at googlegroups.com [mailto:e-prime at googlegroups.com] On Behalf Of ashraf
> > > Sent: 30 March 2010 04:27
> > > To: E-Prime
> > > Subject: stimulus location
>
> > >  ,hi groub,I red
> > >    in e-prime user Guide In appendix B,consideration in research
> > > about   Stimulus Location P.34 that ,a letter displayed 2.5 degrees of
> > > visual angle from fixation will seen Quit poorly,Is this mean ,that
> > > any circle of stimilus in e-prime,its radius greater than2.5  degrees
> > > of visual angle will not be suitable to study attention
>
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