science

Meridian crossing effect

Meridian crossing effect is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Meridian crossing effect rather than just read about it. In short: The meridian-crossing effect is a phenomenon described and evidenced for in the scientific field of visual neuropsychology. It refers to an increase in reaction time to non-attended stimuli located across the vertical meridian, compared to non-attended stimuli located across the horizontal meridian (Huges & Zimba, 1987), i.e., the movement of attention is slower when it has to cross the vertical meridian as compared…

Key takeaways

Meridian crossing effect belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Meridian crossing effect to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Meridian crossing effect from memory before moving on to harder problems.

Reference excerpt

The meridian-crossing effect is a phenomenon described and evidenced for in the scientific field of visual neuropsychology. It refers to an increase in reaction time to non-attended stimuli located across the vertical meridian, compared to non-attended stimuli located across the horizontal meridian (Huges & Zimba, 1987), i.e., the movement of attention is slower when it has to cross the vertical meridian as compared to the horizontal meridian. The horizontal meridian in a visual field extends from the left to the right of the observer. The vertical meridian, on the other hand extends from above the line of sight of the observer to below the line of sight of the observer. The vertical meridian can also be seen as a barrier that differentiates the attended stimuli from the non- attended stimuli. Meridian crossing effect can also be called different-hemifield advantage. According to this, performance rates increase when a task is completed across both the left and right visual hemifields than when performed in a within hemifield version of the task (Sereno & Kosslyn, 1991). A hemifield can be defined as a 170° range of vision that is seen by one eye focusing straight ahead. This should not be confused with bilateral distribution advantage. Different-hemifield advantage mainly holds true only for early perceptual processes. It focuses on the competition for attentional resources in spatial attention. Bilateral distribution advantage on the other hand occurs during more complex or demanding tasks. The Meridian crossing effect was first described by H. C. Huges and L. D. Zimba in the year 1987 in their paper, "Natural boundaries for the spatial spread of directed visual attention".

History The original study by Huges and Zimba started off as an extension of the various studies done revolving around the concept of directed attention, its spatial characteristics and the movement of attention to different locations within the visual field. Their first experiment aimed to determine whether visual performance varied for locations across the vertical and horizontal meridian based on expectancy and to check if attention can be directed both vertically and horizontally. The results showed that cues directed to locations on both the vertical meridian and the horizontal meridian, have similar attentional costs and benefits. Nevertheless, they also reported that subjects have larger decrements in performance when their attention crosses the vertical meridian than when it crosses the horizontal meridian (Huges and Zimba, 1987).

Theoretical context Meridian crossing effect came about as an extension of one of the theories of the spatial structure of attention (Sereno & Kosslyn, 1991).

Shifting focus theories This is one of the oldest theories of the spatial structure of attention. According to this theory, subjects require more time to process targets that occur at unexpected locations as compared to those that occur at expected locations.

Gradient theories According to this theory, resources are processed and made available based on the expectancy of target location, i.e., the farther a stimulus is from the locus of attention, the less processing resources are available (Sereno & Kosslyn, 1991).

Hemifield theories Similar to gradient theories, hemifield theories also predict a gradient of attention. However this gradient is spread out throughout the visual hemifield in which the target is expected. This therefore, is a benefit to that hemifield and a disadvantage to the opposite hemifield (Sereno & Kosslyn).

Neurobiological bases One of the proposed reasons for the decrease in performance when attention crosses the vertical meridian is the shifting of processing of the information from one cerebral hemisphere to the other, across the corpus callosum (Huges & Zimba, 1987). According to Downing and Pinker (1985), on the other hand, decrements in attention when it crosses the vertical meridian can be attributed to the crossing of the foveal region, i.e., the attentional gradient becomes steeper at the fovea. Therefore, two points which are equally distant from each other seem farther apart at the foveal region as compared to when within the same boundary (Downing and Pinker, 1985).

Cognitive bases On the basis of the experiments conducted by Sereno and Kosslyn (1991), in which participants were confronted with two briefly presented stimuli either in one visual hemifield or in the left and right visual hemifields, they argued that the different-hemifield advantage may result from separate, hemisphere-specific pools of attentional capacity operating during perceptual encoding, leading to twice as many resource pools being available during task performance across both hemifields. Processing multiple stimuli that are presented within one hemifield is suggested to lead to high intrahemispheric competition for common processing structures and low interhemispheric competition for representation and requires hemisphere specific processes to take place in parallel (Sereno & Kosslyn, 1991). But the extent to which these pools of processing information impact attention has not been accounted for. Further research needs to be done to understand the causes of this different hemifield advantage.

References

Worked examples

Example 1 — a first encounter with Meridian crossing effect

Start with the simplest possible case. Write down what Meridian crossing effect claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Meridian crossing effect before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Meridian crossing effect ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Meridian crossing effect

In research: Meridian crossing effect appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Meridian crossing effect in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Meridian crossing effect is common in secondary-school and first-year university syllabi. It links to neighbouring topics Phenomena, so understanding it makes those chapters shorter.
In everyday life: Look for Meridian crossing effect outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Meridian crossing effect in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Meridian crossing effect means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Meridian crossing effect out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Meridian crossing effect in simple terms?

Why does Meridian crossing effect matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Meridian crossing effect?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Meridian crossing effect.