Misunderstanding text, need help!

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Hello. I was reading an article about Stiles-Crawford effect, and some information is not clear for me. Can you help me and write this para in another way:
To ensure that the the cone population tested was homogeneous, a small brief test flash, brought into eye through the center of the pupil, was placed at the threshold by varying the intensity of a large adapting field.
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Actualy, I don't understand what did they mean here: "...brought into eye through the center of the pupil, was placed at the threshold by varying the intensity of a large adapting field."

Thanks.

Originally Posted by socean

Hello. I was reading an article about Stiles-Crawford effect, and some information is not clear for me. Can you help me and write this para in another way:
To ensure that the the cone population tested was homogeneous, a small brief test flash, brought into eye through the center of the pupil, was placed at the threshold by varying the intensity of a large adapting field.
--------
Actualy, I don't understand what did they mean here: "...brought into eye through the center of the pupil, was placed at the threshold by varying the intensity of a large adapting field."

Thanks.

You must be reading the Norton/Bailey text. It's not very well written in terms of understandability, in my opinion (and that of just about anyone else who's ever read it.) I suggest getting a copy of Schwartz, "Visual Perception." It's more clinically relevant and written in a manner that can be far more easily understood. The Norton text is not the best way to learn about visual function. It's really more appropriate for research students. I have no idea why any OD program uses it.

Don't overthink Stiles-Crawford. The theoretical experiments modeled in the Norton text are more complex than the principals they are designed to illustrate. If you don't have access to the Schwartz text, 10 or 15 minutes on google will go a long way in understanding it.

Originally Posted by Jason K

You must be reading the Norton/Bailey text. It's not very well written in terms of understandability, in my opinion (and that of just about anyone else who's ever read it.) I suggest getting a copy of Schwartz, "Visual Perception." It's more clinically relevant and written in a manner that can be far more easily understood. The Norton text is not the best way to learn about visual function. It's really more appropriate for research students. I have no idea why any OD program uses it.

Don't overthink Stiles-Crawford. The theoretical experiments modeled in the Norton text are more complex than the principals they are designed to illustrate. If you don't have access to the Schwartz text, 10 or 15 minutes on google will go a long way in understanding it.

Agreed: Schwartz's book is quite good.

Well, I understand that the text I am to read is not the best to understand, however I have to read it. And my question is still the same. The meaning of the word "threshold" is realy misleading me. Can you, at least, say me what does that "threshold" mean??

Originally Posted by socean

Well, I understand that the text I am to read is not the best to understand, however I have to read it. And my question is still the same. The meaning of the word "threshold" is realy misleading me. Can you, at least, say me what does that "threshold" mean??

I don't have a copy of Norton/Bailey anymore, so it's difficult to tell exactly what text is saying out of context. What matters is that you understand the concepts, not necessarily the individual details of the theoretical experiments in that particular text.

What I'm suggesting is that you learn the concepts from another source, Schwartz is a good example, and then return to the Norton/Bailey text after you "get it." You'll find that approach to be helpful in a lot of situations in which one text is not particularly clear on something. Sometimes, looking at it from two different authors' perspectives makes all the difference. Don't get so caught up in the small details that you forget the big picture. That's all I'm saying.

Originally Posted by socean

Well, I understand that the text I am to read is not the best to understand, however I have to read it. And my question is still the same. The meaning of the word "threshold" is realy misleading me. Can you, at least, say me what does that "threshold" mean??

Threshold usually means the maximum amount of a stimulus before evoking a certain effect. At threshold would be the transition point between no evoked effect and an evoked effect.

Such as when drinking beer on an empty stomach. After drinking half a beer and waiting lets say 10 minutes you might not feel anything. Then after this half a beer any amount of beer that you drink you notice that you are slowly becoming intoxicated. Therefore half a beer is your threshold dose.

Originally Posted by Shnurek

Threshold usually means the maximum amount of a stimulus before evoking a certain effect. At threshold would be the transition point between no evoked effect and an evoked effect.

I may be giving too much credit here, but I seriously doubt the OP was confused on the basic definition of a threshold as it relates to individual neurons. He's asking about the use of the word in the context of the theoretical experiment written in Norton/Bailey. C'mon, dude, give your classmate some credit.

I know nothing about the text in question, but a lot of my graduate work was in psychophysics and electrophysiology. This sounds like a psychophysical experiment. An adapting field of some intensity was presented to the subject, followed by or coincident with a test stimulus, the intensity of which would be varied throughout the experiment. The minimum intensity of the test stimulus required for the subject to reliably detect it would define the threshold. By using different adapting fields, you can isolate different visual pathways and determine their thresholds for stimulus detection.

Originally Posted by Visionary

I know nothing about the text in question, but a lot of my graduate work was in psychophysics and electrophysiology. This sounds like a psychophysical experiment. An adapting field of some intensity was presented to the subject, followed by or coincident with a test stimulus, the intensity of which would be varied throughout the experiment. The minimum intensity of the test stimulus required for the subject to reliably detect it would define the threshold. By using different adapting fields, you can isolate different visual pathways and determine their thresholds for stimulus detection.

Visionary is dead on about the experiment. The whole book is basically a lengthy collection of psychophysical experiments. The problem is, the authors sometimes leave out necessary explanations and clarifications.

What is almost certainly confusing to the OP is the fact that the adapting field is what's being varied, not the test stimulus. In effect, they're talking about using the variation of the adapting field as the means for getting the stimulus intensity to arrive at threshold, which is counterintuitive to someone learning the subject since they probably assume the test stimulus would be the variable.

Here's what they could have said that I think might have been a little clearer:

"We chose a small, brief stimulus of a certain intensity and then varied an adapting field until the test stimulus was right at threshold, given that particular adapting field." They assumed that the reader would necessarily understand that threshold would vary in relation to the changing field. It's an obvious point, but it's worded strangely and someone reading it for the first time might not get that from the text.

Originally Posted by Jason K

Visionary is dead on about the experiment. The whole book is basically a lengthy collection of psychophysical experiments. The problem is, the authors sometimes leave out necessary explanations and clarifications.

What is almost certainly confusing to the OP is the fact that the adapting field is what's being varied, not the test stimulus. In effect, they're talking about using the variation of the adapting field as the means for getting the stimulus intensity to arrive at threshold, which is counterintuitive to someone learning the subject since they probably assume the test stimulus would be the variable.

Here's what they could have said that I think might have been a little clearer:

"We chose a small, brief stimulus of a certain intensity and then varied an adapting field until the test stimulus was right at threshold, given that particular adapting field." They assumed that the reader would necessarily understand that threshold would vary in relation to the changing field. It's an obvious point, but it's worded strangely and someone reading it for the first time might not get that from the text.

That IS bad wording. Psychophysics is complicated enough without torquing the wording. I had a heck of a time trying to explain my research to both the medical school and residency admissions committees.